Variables. Arithmetic and Boolean Operations in JavaScript

A variable is a named piece of memory in which you can both store some information and get it from it.

Variables are declared (created) using the var keyword.

// message - variable name var message;

When you create a variable, you can immediately assign a value to it.

Assigning a value to a variable is done using the "=" operator.

// for example, create an email variable and assign the string " [email protected]" var email = " [email protected]"; // set the email variable to a new value email = " [email protected]";

To get the value of a variable, simply refer to it by name.

// for example, display the value of the email variable in the browser console: console.log(email);

To declare more than one variable with the same var keyword, you must use a comma.

Var price = 78.55, quantity = 10, message;

JavaScript is a dynamically or weakly typed language. This means that when declaring a variable, it does not need to specify the type of data it can take. Therefore, a variable can be placed first with a value of one data type, and then another.

var output = "success"; // variable has string data type output = 28; // the same variable, but already having the data type "number" output = true; // the same variable, but already storing a boolean value

Variable value can be changed unlimited quantity once.

// variable age created var age; // variable age is set to 67 age = 67; // variable age is set to "Retirement age" age = "Retirement age"; // variable age is set to 55 age = 55;

It is good practice when developing client-sides to use only one data type in a particular variable, i.e. do not store values ​​that have different data types in a variable. To understand what type of data to expect in a variable, it is recommended to immediately initialize it with a certain value when creating a variable.

The variable name can be composed of letters, numbers, and the symbols $ and _. The first character of the variable must not be a digit. In addition, reserved words cannot be used as a variable name.

// creating two variables, the first variable is called phone, the second is meassage; var phone, message;

The case of letters in a variable name matters. That is, for example, the variable phone and Phone are two different variables.

If strict mode is not used, then you can create a variable with the initial value without the var keyword.

Price = 250.00; // created a variable and initialized it with a number 250.00 percent = "20%"; // created a variable and initialized it with the string "20%"

But creating variables in this way is not recommended.

Data types

In JavaScript, data types can be divided into primitive and object types.

Variables containing primitive data types store the value explicitly.

There are 5 primitive data types in JavaScript:

• number (number);
• string (string);
• boolean type (boolean);
• null;
• undefined.

If one variable is assigned a value to another that contains a primitive data type, then it will get its own copy of that value.

Var x = 77, y = x; x=55; y; // 77

Variables containing an object do not actually store the object itself, but a reference to it.

If one variable is assigned the value of another, which contains an object (a reference to it), then it will also receive a reference to it. As a result of this operation, these two variables will contain a reference to the same object.

// example 1 (with data type "object") var coord1 = (x: 77, y: 100), coord2 = coord1; coord1.x = 55; // set the x property of the object to a new value coord2.x; // 55 because coord1 and coord2 contain a reference to the same object // example 2 (with data type "array") var coord1 = , coord2 = coord1; coord1 = 55; // set the element with index 0 to a new value coord2; // 55 because coord1 and coord2 contain a reference to the same object // example 3 (with data type "date") var date1 = new Date(2018,00,01), date2 = date1; date2 = date2.setDate(date2.getDate()+7); // increment the date by 7 days date1; // 01/07/2018, because date1 and date2 contain a reference to the same object

Number (number)

The numeric type in JavaScript data is generic. It is used to represent both whole and fractional numbers.

varint = 5; // integer var float = 5.98; // fractional number

The number representation format in JavaScript is in accordance with the IEEE 754-2008 standard.

Integers in JavaScript can be specified not only in decimal, but also in octal (0) or hexadecimal number system (0x) using the prefixes given in parentheses:

varint = 010; // 8 int = 055; // 45 int = 0xFF; //255 int = 0xB8; // 184

You can write numbers in exponential form:

varnum = 2e3; // exponential notation for the number 2*10^3 (2000) num = 2e-3; // exponential notation for the number 2*10^-3 (0.002) num = 3.2e3; // 3200 num = 1.5e-2; // 0.015

The numeric data type, in addition to numbers, also contains special numeric values:

• Infinity (positive infinity);
• -Infinity (negative infinity);
• NaN (Not a Number).

The special value Infinity means a very large positive number, i.e. a number that cannot be represented in JavaScript because it is too large.

The special values ​​-Infinity means, on the contrary, a very large negative number, i.e. a number that cannot be represented by JavaScript because it is also too large.

An example of expressions as a result of which the calculation will be returned special numeric values:

5/0; // Infinity -5/0; // -Infinity Math.pow(10,399); // Infinity(10 to the power of 399) Math.pow(10,399); // -Infinity (-10 to the power of 399)

The NaN value is returned as a result of mathematical operations that JavaScript cannot calculate.

5 - "Hi"; // NaN (subtract a line from the number 5) 1000 / "20px"; // NaN (number divided by string) true * "1rem"; // NaN (boolean value true multiply by string)

That being said, it's very interesting that the NaN value in JavaScript is not equal to anything including itself.

NaN == NaN; // false NaN === NaN; //false

Boolean data type (Boolean)

Boolean is a primitive data type that has only two values: true (true) and false (false).

Var a = true; varb=false;

String

String is a data type used in JavaScript to represent text.

JavaScript string can be 0 or more characters.

JavaScript always uses Unicode as the string format.

The creation of a string (string literal) is done by enclosing the text in single or double quotes .

JavaScript; "ECMAScript";

In JavaScript, there is no difference between single and double quotes.

But, in some cases it makes sense to use single quotes rather than double quotes and vice versa.

For example, when a string contains double quotes, it is more convenient to enclose it in single quotes. This will eliminate the need to escape double quotes in it.

"ECMAScript"; // without escaping (using single quotes) "\"ECMAScript\""; // escaped

A string in JavaScript can contain Special symbols. For example, \n (line feed), \t (tab), \r (carriage return), etc.

"This is a sentence.\nThis is also a sentence, but it will start on a new line.";

With strings, you can perform the operation of addition (union) or, in other words, concatenation. The "+" operator is used for this. The meaning of this operation is to append the second string to the end of the first.

"I love " + "JavaScript"; // I love JavaScript

Meaning "undefined"

undefined is a special primitive data type that has a single value equal to undefined .

This data type has a declared variable that has not yet been assigned a value.

Varnum; // undefined

The undefined value will also be returned when accessing a non-existent object property.

var obj = (); // empty object obj.prop; // undefined

Value "null"

null is a special primitive data type that has one value, null .

null is just a special value that has the meaning of "nothing" or "unknown value" i.e. it obviously doesn't mean anything.

Object

An object is a data structure consisting of name-value pairs.

An object is created using object literal notation as follows:

( name_1: value_1, name_2: value_2, name_3: value_3, ... )

As you can see, the name is separated from the value using a colon, and the pairs are separated from each other using a comma.

Moreover, if a function acts as the value of a pair, then it is called a method of this object. All other pairs, i.e. pairs that do not use a function as a value are called object properties.

In other words, an object is a data structure consisting of properties and methods.

Var person = ( name: "Vitaly", age: 27, getAge: function () ( return "Age: " + this.age; ) )

Access to the properties of an object is performed through a dot or by means of bracket notation.

// display the value of the age property in the browser console // 1 way (through a dot) console.log(person.age); // 2nd way (using brackets) console.log(person["age"]); // call the getAge method; the value it will return will be output to the console console.log(person.getAge());

typeof operator

The typeof operator is used to obtain information about the data type of an expression as a string.

The syntax for the typeof operator (the version without the parentheses):

typeof expression

The syntax for the typeof operator (using parentheses):

typeof(expression)

Varname, age=37, email=" [email protected]", isLicense = true, interest: null, lastExperience: ( period: "June 2011 - June 2018", place: "ISACA, Moscow", position: "Web designer" ), getExperience: function() ( return lastExperience.period + " ("+ lastExperience.position + " - " + lastExperience.place + ")"; ); typeof name; // "undefined" typeof age; // "number" typeof isLicense; // "boolean" typeof interest; / / "object" (1) typeof lastExperience; // "object" typeof getExperience; // "function" (2) /* (1) is a bug that has been present in the language since its first implementation; it has not been fixed for compatibility purposes and should be taken into account when writing scripts; null is a primitive data type, it is not an object */ /* (2) - it is very convenient that the typeof operator separates functions separately; but a function in JavaScipt is also object; this can be easily seen if you execute the following construction: */ typeof getExperience.__proto__.__proto__ // "object" (the function prototype is an object)

Constants

With the release of ECMAScript 6, it became possible to create constants. This is done using the const keyword.

Const COLOR_RED = "#ff0000";

A constant is a variable whose value is protected from being changed. Those. attempting to change the value will throw an error.

Const COLOR_RED = "#ff0000"; COLOR_RED = "#f44336"; // Uncaught TypeError: Assignment to constant variable.

If, for example, a constant contains an object, then it cannot be changed, or rather a reference to it. But the properties of this object can be changed.

Const COLORS = ( red: "#ff0000", green: "#00ff00", blue: "#00ff00" ) COLORS = ["#ff0000","#00ff00","#00ff00"]; // Uncaught TypeError: Assignment to constant variable. COLORS.green = "#4caf50";

To be honest, I did not want to introduce this topic from the beginning. What can be said about variables, especially in JavaScript? But then I remembered how sometimes I dealt with complex constructions and had difficulty understanding some expressions that seemed to be unacceptable in other programming languages. You can say this: here you will not get the "Invalid data type" error, and if it does, it will be very rare. If you have worked with other programming languages, then remember how often you had an error about incorrect data types. In JavaScript, a data type can be easily overridden without you noticing where, and that's where it gets tricky. On the other hand, if you are well versed in the principles of type conversions, know all the properties of variables and arrays, these features will only bring you confidence in writing programs.

JavaScript variables can store values ​​of various types:

• Strings - a sequence of characters;
• Numeric values ​​- integers and real numbers;
• Boolean values ​​are just two values ​​true or false;
• Arrays are sets of variables of the same type;
• Dates are date and time values.

The lifetime of a variable is related to the window in which they are created and depends on where they are defined. JavaScript programs are contained in HTML documents, and when a new document is loaded into the browser, any variables created in the program will be removed.
To save any values ​​when loading a new document in JavaScript, there are only 2 solutions:

• by creating variables in the frame-containing document top level;
• by using "cookies";

To store variables and functions using framed documents, these variables and functions must be defined in the top-level document and then use the parent or top properties. window object to access them from documents loaded in frames. IMPORTANT: such variables and functions must be set in the head of the top-level document between the tags . . . . Of course, there is a possibility that the document can be loaded without a frame, and then accessing an undefined object will cause an error, but you can first check whether the document is loaded into a frame:

Cookies allow small pieces of information to be stored on local disk user. By setting cookie values ​​and sorting them out at subsequent stages of work, you can restore the necessary values. We will talk more about cookies later.

Variable names, creating variables

It is much easier to create a variable in JavaScript than in other programming languages. For example, when creating a variable, it is not necessary to specify its type. Variables are defined with or without initial values. During program execution, already created variables can even be cast to different data types. Variable names can start with any letter (a through z, or A-Z) or underscore (_), the remainder can contain numbers, underscores, and letters. Remember that variable names distinguish between upper and lower case characters: for example MyVariable is not the same as myvariable.
A variable can be created in one of the following ways:

• using the var operator and the assignment operator (=);
• using the assignment operator (=).

The Var operator is used not only to create a variable, but also to initialize it. The assignment operator (=) is required to store a value in a variable, and is not necessary when working with variables created without an initial value. For example:

VarMyVariable = 35

Creates a variable named MyVariable containing the numeric value 35. The variable exists as long as the current document is loaded. If you create this variable in a top-level framed document, it should be accessed using the top.MyVariable expression, or even better parent.MyVariable to protect against nested frames.

In language JavaScript variables can be overridden, even specifying a different data type. For example, after executing the statement

Var MyVariable = "35"

The variable will already store the string "35". Such transformations sometimes lead to misunderstandings. For example:

What value do you think the variable "c" will take after the program is executed? If you are not familiar with the rules for converting variables in JavaScript, you will not guess. The value of the variable "c" after the completion of the block will be equal to the numerical value 320. We will talk about the principles of variable type conversion later. A variable can be defined without using the "Var" operator, but simply assigning a value, and what type of data will be assigned, that type will be a variable. The "Var" operator is mainly used for the readability of a JS program. A variable can also be set without initial values, for example:

VarMyVariable;

A variable named MyVariable has been created with no defined data type and no initial value. Variables created using such declarations are known as null variables. For example, comparing such a variable with null, you can find out if the variable is defined. However, one should not confuse different things: "" - an empty string is a string type and not a null value at all.

The type of a variable can be set anywhere in a JS program, unlike other programming languages, which gives you more flexibility, but also the possibility of confusion - remember this. A variable that has not been created cannot be accessed. If you want to create a temporary variable, such as a loop counter, you need to prefix it with var:
for (var i=0; i<= document.links.length; i++) {
. . . . .
}
in this example, the variable i is initialized and then used as the counter of the for statement.
Variables defined with var are separated by a comma. For greater readability of a JS program, each variable is usually written on a new line.

String variables

A string is a set of characters enclosed in single or double quotes. Strings in JavaScript are treated as objects. This is by far the most common kind of object, so JavaScript has many standard functions for manipulating strings. You can create a String object in one of several ways:

• assigning a value using the String() constructor;
• using the Var operator and the assignment operator to create and initialize a string;
• creation and initialization of a string variable in an assignment statement;
• converting a variable of a numeric type by adding to a string type (10+"" ==> "10");

The simplest and most common way to create a String object is to use operators like

Var myVariable = "Good beer";

The above statement assigns the string "Good beer" to the string variable myVariable. The variable myVariable is treated as a string object and can use any of standard methods JavaScript String object. The Var operator can be skipped, as mentioned earlier, it is needed mainly for the readability of the program.

To create string objects, you can use the String() constructor with operator new. In fact, the String object is not a JavaScript language object, but a built-in object of the browser, mainly because strings are created when the user needs them. Consider an example:

Var myVariable = new String();

This statement creates a new object - an empty string named myVariable. Initially, it is an empty string (""), and the value of the myVariable.length property is 0.

The String() constructor accepts a given string as an argument:

Var myVariable = new String("Correct beer");

A string object can contain special characters that control string formatting:

• \n - newline character;
• \r - carriage return character;
• \f - transition code to a new page;
• \xnn - character representation as hexadecimal ASCII code nn;
• \b - key code.

these characters will only be interpreted correctly in containers and in the "Alert" methods. The formatting for document.write() is done by other methods or HTML tags. <br>The String object has only one property, length, whose value is the number of characters in the string contained in the object. The methods of the String object can be divided into two categories: <ul><li>HTML document formatting methods;</li><li>string processing methods.</li> </ul> Document formatting methods are used to output strings to a document, and string manipulation methods are used to inspect and modify the contents of a String object. <br>Here is a list of methods: (the letter F - formatting methods, and the letter Y - string management) <table border="1"><tbody><tr><td>Method</td> <td> </td> <td>Description</td> </tr><tr><td>anchor()</td> <td>At</td> <td>Creates a named label, i.e. tag <a name>from object content</td> </tr><tr><td>big()</td> <td>F</td> <td>Wraps a string in a container <big> . . . </big>, to display in large font</td> </tr><tr><td>blink()</td> <td>F</td> <td>Wraps a string in a container <blink> . . . </blink> to display it flashing.</td> </tr><tr><td>bold()</td> <td>F</td> <td>Wraps a string in a container <b> . . . </b> to display it in bold.</td> </tr><tr><td>charAt()</td> <td>At</td> <td>Returns the character at the given position in the string</td> </tr><tr><td>fixed()</td> <td>F</td> <td>Wraps a string in a container <tt> . . . </tt> to display it in a constant-width font.</td> </tr><tr><td>fontcolor()</td> <td>F</td> <td>Wraps a string in a container <font color=colorCode> . . . </font> to display it in a specific color.</td> </tr><tr><td>fontsize()</td> <td>F</td> <td>Wraps a string in a container <font size=fontSize> . . . </font> to display it in a specific font size.</td> </tr><tr><td>IndexOf()</td> <td>At</td> <td>Returns the index of the first given character found in the string.</td> </tr><tr><td>italics()</td> <td>F</td> <td>Wraps a string in a container <i> . . . </i> to display it in italics.</td> </tr><tr><td>lastIndexOf()</td> <td>At</td> <td>Returns the index of the last given character found in the string.</td> </tr><tr><td>link()</td> <td>At</td> <td>Creates a hyperlink tag <a href> . . . </a> and puts the contents of the object into it</td> </tr><tr><td>small()</td> <td>F</td> <td>Wraps a string in a tag <small> . . . </small> to display it in a smaller font size.</td> </tr><tr><td>strike()</td> <td>F</td> <td>Wraps a string in a container <strike> . . . </strike> so that it appears as a strikethrough.</td> </tr><tr><td>sub()</td> <td>F</td> <td>Wraps a string in a container _{. . .} to display as a subscript.</td> </tr><tr><td>substring()</td> <td>At</td> <td>Returns a substring of a text string.</td> </tr><tr><td>sup()</td> <td>F</td> <td>Wraps a string in a container ^{. . .} to display it as a superscript.</td> </tr><tr><td>toLowerCase()</td> <td>At</td> <td>Converts all letters of a string to lowercase</td> </tr><tr><td>toUpperCase()</td> <td>At</td> <td>Converts all letters of a string to uppercase</td> </tr></tbody></table><p>Numeric variables</p><p>Numeric values ​​can be either integers or floating point numbers. Floating point numbers are called real or real. The following operations are applicable to numerical values:</p><ul><li>multiplication (*);</li><li>divisions (/);</li><li>addition (+);</li><li>subtraction (-);</li><li>magnification (++);</li><li>decrease(--);</li> </ul> In addition, the operations of multiplication, division, addition, and subtraction are used in combination with assignment (*=, /=, +=, -=), as well as methods <a href="https://zhumor.ru/en/internet/metody-okrugleniya-chisel-v-javascript-obekt-math-v-javascript---metody-round-ceil-i-floor--.html">Math object</a>. <p>Boolean variables</p><p>Boolean or logical variables contain only literal values ​​- true and false - and are used in <a href="https://zhumor.ru/en/computer/postroenie-logicheskih-shem-po-logicheskomu-vyrazheniyu-opredelenie-signala-na-vyhode-logicheskoi-shemy.html">logical expressions</a> and operators. <br>To check the value of a boolean variable, the logical equality operation is also used: <br>booleanVar == true <br>although in this case such a verification operation is redundant. To check for values ​​that are not true, use the logical negation sign (!). For example, the !booleanVar expression will return true if booleanVar is false. Instead of the words "true" and "false", you can use the numeric values ​​"1" and "2", since these are the Boolean values ​​that are represented in the computer's memory: 1==true and 0==false.</p><p>Array variables</p><p>Array variables contain ordered collections of values ​​of the same type, presented as a single variable for convenience. Many standard JavaScript document property objects, such as hyperlinks and labels, are arrays. In JavaScript, an element of an array should be accessed using an expression:</p><p>ArrayName</p><p>Where arrayName is the name of the array and index is a numeric variable or a number that specifies the element's position in the array. For example, arrayName is the first element of this array. Array indexes in JavaScript start from zero. Array elements can be of any type, such as strings or booleans. In addition, under certain conditions, an array can contain elements of various data types. In language <a href="https://zhumor.ru/en/internet/kak-sozdat-associativnyi-massiv-v-javascript-jquery---perebor-massiva.html">JavaScript arrays</a> created with:</p><ul><li>constructor Array();</li><li>constructor Object();</li><li>user-defined constructor.</li> </ul> The Array() constructor not only creates an array object, but also assigns initial values ​​to its elements. It is possible to add elements to an array dynamically - by assigning <a href="https://zhumor.ru/en/internet/js-udalit-element-massiva-znacheniyu-javascript---elementov---udalit.html">certain values</a> array elements. It is also allowed to "skip" array elements and set them in any order. To create a new instance of an array object, the Array() constructor must be used with the new operator. For example, the following example creates an array named arrayImg containing two elements, each of which is a String object <p>var path = "c:/images/" , <br>arrayImg = new Array(); <br>arrayImg = path+"img1.gif"; <br>arrayImg = path+"img2.gif";</p><p>When using the Array() constructor, the value of the length property is set automatically. Therefore, after initializing the array elements in the above example, the expression arrayImg.length returns the value 2. The array elements can also be given as constructor parameters:</p><p>var path = "c:/images/" , <br>arrayImg = new Array(path+"img1.gif", path+"img2.gif");</p><p>This expression is a shorthand for the previous example. <br>In JavaScript, you can create an array, this is an array in which the elements have <a href="https://zhumor.ru/en/internet/kak-menyat-lampy-v-ofise-kak-pravilno-razobrat-lampochku.html">different type</a> data:</p><p>Var myArray = new Array(3.14, true, 85, date(), "word");</p><p>Creates an array whose myArray element is a float, myArray element is a Boolean value, and myArray element is a Date object. <br>The size of the array, and therefore the value of the length property of the object created by the Array() constructor, depends on the maximum index value that was used to specify the array element. For example:</p><p>Var myArray = new Array; <br>myArray = "This is the 21st element of the array";</p><p>The twenty-first element of the array is set to the string value "This is the 21st element of the array", and the value of the myArray.length property is 21, regardless of whether the values ​​in the array are less than 20. <br>The value of the length property of an Array object is automatically set when you explicitly specify the number of elements in the Array() constructor:</p><p>MyArray = new Array(10);</p><p>The statement creates an array of 10 elements from 0 to 9. The length property of an array cannot be set by assignment because length is a read-only property. For example, to set the value 10 for the length property, you only need to specify the value of the last, in this case, the 9th element of the array:</p><p>MyArray = new Array(); <br>myArray = 0;</p><p>In addition, it is possible to set the values ​​of the array elements when constructing it:</p><p>MyArray = new Array(0,0,0,0,0,0);</p><p>Object() constructor</p><p>The terms object and array are interchangeable, although the Object() and Array() constructors work differently. It is not possible to pass multiple array elements to the Object() constructor, so this expression <br>var myObj = new Object(value1, value2); <br>will not work. Arrays created with the Object() constructor do not have a length property. Therefore, when creating an array in this way, you should either traverse the array with a for loop and count the elements of the array, or hardcode the length of the array as the value of its first element (usually done by modeling the length property), and then access it as necessary to check the size of the array, increasing the value when a new element is added, and also as a loop parameter when cyclically reading or changing the values ​​of elements. Such an object is often unacceptable for cases where the contents of an array must change dynamically, so in most cases the Array() constructor is used. Array index values ​​created in the Object() constructor also start at zero. To create an array using the Object() constructor, it is customary to use a notation of the form:</p><p>Var myObj = new Object(); <br>myObj = 2; // set the dimension of the array <br>myObj = "First element"; <br>myObj = "Second element";</p><p>To find out the size of an array created in this way, you need to refer to the element myObj. The value of the myObj.length property is null, since the value is undefined.</p><p>Converting strings and numbers</p><p>Finally came to the most interesting topic. The fact is that in JavaScript, unlike other languages, there are no functions like Val() and Str(). Once I saw a JavaScript program, I won't name the author, where with the help of various data type conversions there was an attempt to confuse the program for "non-advanced" users. So, there are two rules to remember:</p><ul><li>The conversion of a number into a character string is done by adding the numeric argument to the string argument, regardless of the permutation of the terms. For example, if the variable is varI=123, then you can convert the variable and hence its value into a character string: varI = varI + "" or vice versa: varI = "" + varI. If added to a non-empty string: varI = varI + "456", then the result of the value of the variable varI will be "123456". The same is true and vice versa: varI = "456" + varI - result: "456123";</li><li>A string is converted to a number by subtracting one operand from the other, also regardless of their position. For example, if the variable varI = "123", then you can convert it to a number if you subtract the values ​​0 from it: varI = varI - 0, and accordingly the value of the variable from the string type is converted to numeric: 123. When rearranging the operands, respectively, the sign of the numeric value will change to opposite. Unlike converting a number to a string, subtraction operations cannot use literal values. So if "JavaScript" + 10 turns into varI == "JavaScript10", then an operation like varI = "JavaScript" - 10 will return the value "NON" - that is, such an operation is not allowed. And yet, when subtracting a string value from a string value, a transformation also occurs: varI = "20" - "15", the value of the varI variable will be the number 5.</li> </ul> <p>Variables</p><h2>Declaring Variables</h2> <p>Before a variable can be used in JavaScript, it must be declared. Variables are declared with a keyword <b>var</b> in the following way:</p> <p>Vari; varsum;</p> <p>Once using <a href="https://zhumor.ru/en/internet/kak-podobrat-klyuchevye-slova-prodvizheniya-chto-takoe-klyuchevye-slova-i-kak-ih.html">keyword</a> var, you can declare multiple variables:</p> <p>Declaring variables can be combined with their initialization:</p> <p>varmessage = "hello"; var i = 0, j = 0, k = 0;</p> <p>If a <a href="https://zhumor.ru/en/internet/spisok-uchitelei-nachalnyh-obuchenie-na-uchitelya-nachalnyh-klassov.html">initial value</a> var is not specified in the statement, then the variable is declared, but its initial value remains undefined (undefined) until it is changed by the program.</p> <p>If you are familiar with programming languages ​​with static data types, such as C# or Java, you may notice that there is no type declaration in variable declarations in JavaScript. Variables in JavaScript can store values ​​of any type. For example, in JavaScript it is possible to assign a number to some variable, and then assign a string to the same variable:</p> <p>Vari = 10; i = "hello";</p> <p>Using the var statement, you can declare the same variable multiple times. If the redeclaration contains an initializer, then it acts like <a href="https://zhumor.ru/en/internet/mozhno-li-zagruzochnuyu-fleshku-sdelat-obychnoi-instrukciya-po.html">ordinary instruction</a> assignments.</p> <p>If you try to read the value of an undeclared variable, JavaScript will generate an error. In ECMAScript 5 strict mode, an error is also raised when trying to assign a value to an undeclared variable. However, historically and when executing in non-strict mode, if you assign a value to a variable that is not declared with a var statement, then JavaScript will create that variable as a property of the global object, and it will act in much the same way as a well-declared variable. This means that global variables need not be declared. However, this is considered a bad habit and can be a source of error, so always try to declare your variables with var.</p> <h2>Variable scope</h2> <p>The scope of a variable is the part of the program for which the variable is defined. A global variable has a global scope - it is defined for the entire JavaScript program. At the same time, variables declared inside a function are defined only in its body. They are called local and have local scope. Function parameters are also considered local variables, defined only in the body of that function.</p> <p>Within a function body, a local variable takes precedence over a global variable of the same name. If you declare a local variable or function parameter with the same name as a global variable, then the global variable will actually be hidden:</p> <p>varresult = "global"; function getResult() ( var result = "local"; return result; ); console.log(getResult()); // Display "local"</p> <p>When declaring variables with global scope, the var statement can be omitted, but when declaring local variables, you should always use the var statement.</p> <p>Variables are a fundamental part of many programming languages; they are one of the most important concepts for beginner programmers. There are many different properties of variables in JavaScript, as well as several rules to follow when naming them. JavaScript has three keywords used to declare a variable - var , let and const - and each of them affects how the variable will be interpreted in the code.</p> <p>This tutorial will introduce you to variables, teach you how to declare and name them, and explain the difference between var, let and const. In addition, you will learn what variable hoisting is and how scope affects the behavior of a variable.</p> <h2>What are variables</h2> <p>A variable is a named piece of memory used to store <a href="https://zhumor.ru/en/internet/tablica-oboznacheniya-cvetov-cvet-v-stilyah-mozhno-zadavat-raznymi.html">different values</a>. A piece of information that can be referenced multiple times can be stored in a variable for later use or modification. In JavaScript, the value contained within a variable can be any data type, including a number, string, or object.</p> <p>Prior to the ECMAScript 2015 (ES6) language specification on which JavaScript is based in <a href="https://zhumor.ru/en/internet/prilozhenie-kamera-zapisyvaet-audio-v-dannyi-moment-prilozhenie.html">this moment</a>, there was only one way to declare a variable, and that was with the var keyword. This is why most old codes and manuals only use var to declare variables. Let's look at the differences between var, let and const.</p> <p>The var keyword allows you to demonstrate the concept of the variable itself. In the example below, we are declaring a variable and assigning a value to it.</p> <p>// Assign the string value 8host to the username identifier <br>var username = "8host_blog";</p> <p>This expression has several parts:</p> <ul><li>Declaring a variable using the var keyword;</li> <li>Variable name (or identifier), username;</li> <li>The assignment operator, represented by the syntax =;</li> <li>The value to assign, "8host_blog".</li> </ul><p>Now you can use the username variable in your code. JavaScript will remember that username represents the value 8host_blog.</p> <p>// Check if variable is equal to value <br>if (username === "8host_blog") ( <br>console log(true); <br> } <br>true</p> <p>As mentioned earlier, variables can be expressed with any JavaScript data type. In this example, variables are expressed as string, number, object, boolean, and null.</p> <p>// Assignment of various variables <br>var name = "Morty"; <br>var spartans = 300; <br>var kingdoms = [ "mammals", "birds", "fish" ]; <br>var poem = ( roses: "red", violets: "blue" ); <br>var success = true; <br>var nothing = null;</p> <p>Using console.log, you can view the value of any variable:</p> <p>// Send spartans variable to the console <br>console log(spartans); <br> 300</p> <p>Variables store data in memory that can later be used or changed. Variables can also be reassigned and given a new value. The simple example below demonstrates how a password can be stored in a variable and then updated.</p> <p>// Assign value to password variable <br>var password = "hunter2"; <br>// Reassign variable value with a new value <br>password = "hunter3"; <br>console log(password); <br>hunter3</p> <p>AT <a href="https://zhumor.ru/en/internet/kakie-programmy-mozhno-skachat-dlya-zarabatyvaniya-realnye-avtomaticheskie-programmy-dlya-zarabotka-den.html">real program</a> the password is likely to be securely stored in the database. However, this simple example illustrates a situation in which you can update the value of a variable. The value of the password variable was hunter2, but it has been given a new value, hunter3, and JavaScript will now use the new value.</p> <h2>Variable naming</h2> <p>In JavaScript, variable names are called identifiers. Several rules for naming identifiers can be found in the manual. Here they are in short:</p> <ul><li>Variable names can only contain letters, numbers (0-9), dollar signs ($), and underscores (_).</li> <li>Variable names cannot contain whitespace characters.</li> <li>The variable name must not start with a number.</li> <li>There are several reserved keywords that cannot be used as variable names.</li> <li>Variable names are case sensitive.</li> </ul><p>JavaScript also has a convention for using camel case (camelCase) in the names of functions and variables declared with var or let. In this case, the first word is written in <a href="https://zhumor.ru/en/computer/kakoi-element-ustanavlivaet-verhnii-indeks-delaem-v-css-verhnii-registr.html">lower case</a>, and each following word starts with a capital letter (words are written without spaces between them). Most variables that are not constants will follow this convention, with a few exceptions. Variable names that are constants (declared with the const keyword) are usually written as <a href="https://zhumor.ru/en/computer/nadstrochnyi-znak-html-html---eto---kak-sdelat-tekst-v-verhnem-registre.html">upper case</a>.</p> <p>It seems that there are quite a lot of rules, but it seems so only at first glance. By working with JavaScript frequently, you will quickly memorize them.</p> <h2>Difference between var, let and const</h2> <p>JavaScript uses three different keywords to declare variables, which add an extra layer of complexity. These keywords differ in variable scope, hoisting, and reassignment capability.</p> <p>You may be wondering which of the three keywords you should use in your programs. It's common to use const as often as possible, and let in loops and for reassignment. Typically, var is used in legacy code.</p> <h2>JavaScript scope</h2> <p>Scope in JavaScript refers to the current code context, which determines the accessibility of variables. The scope is local and global:</p> <ul><li>Global variables are those that are declared outside of a block.</li> <li>Local variables are those that are declared within a block.</li> </ul><p>In the example below, we will create a global variable.</p> <p><br>var creature = "wolf";</p> <p>You know that variables can be reassigned. You can create new variables in the local scope with the same name as variables in the outer scope without changing or redefining the original value.</p> <p>The following example creates a global variable species. Inside the function, there is a local variable with the same name. By sending them to the console, you will see that the value of the variable differs depending on the scope, and the original value does not change.</p> <p>// Initialize a global variable <br>varspecies = "human"; <br>function transform() ( <br>// Initialize a local, function-scoped variable <br>var species = "werewolf"; <br>console log(species); <br> } <br>// Log the global and local variables <br>console log(species); <br>transform(); <br>console log(species); <br>human <br>werewolf <br>human</p> <p>In this example, the local variable is scoped at the function level. Variables declared with the var keyword are always in this scope (that is, they recognize functions as having a separate scope). So a local variable is not available in the global scope.</p> <p>However, the new keywords let and const are block-level scoped. This means that a new local scope is created from any block, including function blocks, if statements, and <a href="https://zhumor.ru/en/internet/beskonechnyi-cikl-while-v-bash-skripte-bash-opisanie-ciklov-for-while.html">for loops</a> and while.</p> <p>To illustrate the difference between function and block level variables, create a new variable in an if block with let.</p> <p>var fullMoon = true; <br>// Initialize a global variable <br>let species = "human"; <br>if (fullMoon) ( <br>// Initialize a block-scoped variable <br>let species = "werewolf"; <br><br> } <br><br><br>It is not a full moon. Lupine is currently a human.</p> <p>In this example, the species variable has one global value (human) and one local value (werewolf). However, if you use var, the result will be different.</p> <p>// Use var to initialize a variable <br>varspecies = "human"; <br>if (fullMoon) ( <br>// Attempt to create a new variable in a block <br>var species = "werewolf"; <br>console.log(`It is a full moon. Lupin is currently a $(species).`); <br> } <br>console.log(`It is not a full moon. Lupin is currently a $(species).`); <br>It is a full moon. Lupine is currently a werewolf. <br>It is not a full moon. Lupine is currently a werewolf.</p> <p>As a result, both the global variable and the block-level variable produce the same value, werewolf. This is because instead of creating a new local variable, var reassigns the same variable in the same scope. var doesn't understand that if should be part of a different, new scope. It is generally recommended to declare variables at the block level, as this reduces the risk of inadvertently redefining variable values.</p> <h2>Raising Variables</h2> <p>Most of the examples so far have used the var keyword to declare a variable and initialize the variable with a value. Once declared and initialized, the value can be accessed or the variable can be reassigned.</p> <p>If you try to use a variable before it has been declared and initialized, the result will be undefined.</p> <p><br>console log(x); <br>// variable assignment <br>var x = 100; <br>undefined</p> <p>However, if you omit the var keyword, the variable will not be declared, but only initialized. This will return a ReferenceError and stop script execution.</p> <p>// Attempt to use a variable before declaring it <br>console log(x); <br>// Variable assignment without var <br>x=100; <br>ReferenceError: x is not defined</p> <p>This is due to hoisting - this is a JavaScript behavior in which declarations of variables and functions are moved to <a href="https://zhumor.ru/en/computer/optimizaciya-i-szhatie-css-v-page-speed-kak-otklyuchit-vneshnie-faily-stilei-i.html">upper part</a> their areas. Because only the actual declaration is raised, not the initialization, undefined is returned in the first example.</p> <p>To better demonstrate this concept, we have written <a href="https://zhumor.ru/en/computer/napisat-kod-html-sleduyushchei-tablicy.html">following code</a> and explained how JavaScript reads it:</p> <p>// The code we wrote <br>console log(x); <br>var x = 100; <br>// How JavaScript interpreted it <br>varx; <br>console log(x); <br>x=100;</p> <p>Before executing the script, JavaScript stores x in memory as a variable. Since the variable was called before it was defined, the result is returned undefined, not 100. However, this does not raise a ReferenceError and does not stop the script. While the var keyword didn't actually change the location of var, this demonstrates how hoisting works. This behavior can cause problems because the programmer who wrote this code most likely expects the output x to be true, not undefined.</p> <p>Also, lifting can lead to unpredictable results, as in the following example:</p> <p><br>var x = 100; <br>function host() ( <br>// A condition that should not affect the outcome of the code <br>if (false) ( <br>var x = 200; <br> } <br>console log(x); <br> } <br>host(); <br>undefined</p> <p>In this example, the global variable x is 100. Depending on the if statement, x might change to 200, but since the condition was false, it shouldn't affect the value of x. Instead, x was raised before the start of the hoist() function, and the value became undefined.</p> <p>This unpredictable behavior can cause errors in the program. Because let and const are defined at the block level, they won't be hoisted like the example below.</p> <p>// Initialize x in the global scope <br>let x = true; <br>function host() ( <br>// Initialize x in the function scope <br>if (3 === 4) ( <br>let x = false; <br> } <br>console log(x); <br> } <br>host(); <br>true</p> <p>Duplicate variable declaration, which is possible with var, will fail with let and const.</p> <p>// Attempt to overwrite a variable declared with var <br>var x = 1; <br>var x = 2; <br>console log(x); <br> 2<br>// Attempt to overwrite a variable declared with let <br>let y = 1; <br>let y = 2; <br>console log(y);</p> <p>Uncaught SyntaxError: Identifier 'y' has already been declared <br>So, variables declared with var can be affected by hoisting. Hoisting is a mechanism in JavaScript where variable declarations are kept in memory. This can lead to undefined variables in the code. The let and const keywords solve this problem by throwing an error if you try to use a variable before declaring it or declare a variable more than once.</p> <h2>Constants</h2> <p>Many programming languages ​​use constants, which are values ​​that cannot be changed. That is, values ​​assigned to a constant cannot be reassigned.</p> <p>By convention, const identifiers are written in upper case. This distinguishes them from other variables.</p> <p>In the example below, the SPECIES variable is initialized as a constant using the const keyword. Attempting to reassign a variable will result in an error.</p> <p>// Assign value to const <br>const SPECIES = "human"; <br>// Attempt to reassign value <br>SPECIES = "werewolf"; <br>console log(SPECIES); <br>Uncaught TypeError: Assignment to constant variable.</p> <p>Because const values ​​cannot be reassigned, they must be declared and initialized at the same time or an error will occur.</p> <p>// Declare but do not initialize a const <br>const TODO; <br>console.log(TODO); <br>Uncaught SyntaxError: Missing initializer in const declaration</p> <p>Values ​​that cannot be changed by programming are called immutable, and values ​​that can be changed are called mutable (this is obvious). The values ​​of a constant cannot be reassigned, but they are mutable because the properties of objects declared with const can be changed.</p> <p>// Create a CAR object with two properties <br>const CAR = ( <br>color: "blue", <br>price: 15000 <br> } <br>// Modify a property of CAR <br>CAR.price = 20000; <br>console log(CAR); <br>( color: "blue", price: 20000 )</p> <p>Constants allow you to tell other programmers working on a project, and yourself, that a given variable should not be reassigned. To declare a variable that can be reassigned, use let.</p> <h2>Conclusion</h2> <p>In this tutorial, you learned what a variable is, familiarized yourself with the rules for naming variables, and learned how to reassign their values. You also learned about scopes and variable hoisting, the limitations of the var keyword, and how let and const solve these problems.</p> <p>As in any other programming language, variables are very important. Thanks to variables, the code becomes universal, which allows you to solve more problems. In a nutshell, programming is indispensable without the use of variables.</p> <p>As you already know from the previous article (JavaScript Fundamentals), variables are declared using the keyword <b>var</b>.</p> <p>It is important to note here that <b>case is important</b> when declaring and using a variable. That is a variable <i>var A</i> and variable <i>var a</i> are two different variables. And the name that was originally given to the variable should be used throughout the script.</p> <p>Since JavaScript is a client-side language, the values ​​of variables are stored in <a href="https://zhumor.ru/en/internet/chem-to-zanyata-operativnaya-pamyat-kuda-devaetsya-operativnaya-pamyat.html">RAM</a> user. AT <a href="https://zhumor.ru/en/internet/razdelenie-instrukcii-osnovy-php-kak-razdelyayutsya-instrukcii-v-yazyke.html">PHP language</a> the values ​​are stored in the server's RAM.</p> <h2>How to properly name a variable in JavaScript</h2> <p>Variable names cannot contain special characters such as #, $, hyphen, space, dot, and others. You can only use letters (lowercase recommended), numbers, and the underscore (_) sign.</p> <p>You cannot have a number as the first character in a name. For example, you can call it bmw_93, but you can’t call it 123_opel.</p> <p>Also, you cannot name a variable with reserved words of the language, such as var, for, if.</p> <h3>List of registered words in JavaScript</h3> <table class="table_class"><tr><td>abstract</td> <td>boolean</td> <td>break</td> </tr><tr><td>byte</td> <td>case</td> <td>catch</td> </tr><tr><td>char</td> <td>class</td> <td>const</td> </tr><tr><td>continue</td> <td>default</td> <td>do</td> </tr><tr><td>double</td> <td>else</td> <td>extends</td> </tr><tr><td>false</td> <td>final</td> <td>finally</td> </tr><tr><td>float</td> <td>for</td> <td>function</td> </tr><tr><td>goto</td> <td>if</td> <td>implements</td> </tr><tr><td>import</td> <td>in</td> <td>instanceof</td> </tr><tr><td>int</td> <td>interface</td> <td>long</td> </tr><tr><td>native</td> <td>new</td> <td>null</td> </tr><tr><td>package</td> <td>private</td> <td>protected</td> </tr><tr><td>public</td> <td>return</td> <td>short</td> </tr><tr><td>static</td> <td>super</td> <td>switch</td> </tr><tr><td>synchronized</td> <td>this</td> <td>throw</td> </tr><tr><td>throws</td> <td>transient</td> <td>true</td> </tr><tr><td>try</td> <td>var</td> <td>void</td> </tr><tr><td>while</td> <td>with</td> <td> </td> </tr></table><p>It is recommended to name variables meaningfully so that it is intuitively clear what value is stored in this variable, for example, to store the number of cars, you can use the name count_cars rather than abcsd.</p> <p>It is still impossible to name the variable with Russian letters, only with English ones. It is also recommended to name variables with English words, if you don't speak English well, you can use transliteration for Russian words.</p> <h2>Variable types</h2> <p>Any declared variable is of a particular type. There are several types of data in programming, of which the most important are the following:</p> <ul><li><b>Integer</b>– This type includes whole numeric numbers, both positive and negative (for example: 1,2,4, -8, -100).</li> <li><b>Double</b>– This type includes floating point numbers, they are also called <a href="https://zhumor.ru/en/internet/prostye-pravila-okrugleniya-v-javascript-izuchaem-metody-i-primenyaem-na.html">fractional numbers</a>(e.g. 1.6, -9.8, 2.5). They can also be negative.</li> <li><b>String</b>- These are string values. This type includes any character, any letter or string. All string values ​​must be declared in single or double quotes.</li> <li><b>Boolean</b>– This type is boolean. It can only have one of two values, it is either <b>true</b>(true) either <b>false</b>(False).</li> <li><b>array</b> is the collection of data that can be <a href="https://zhumor.ru/en/computer/samsung-galaksi-ase-gt-svodnyi-obzor-smartfonov-samsung-galaxy-ace-s5830-fit-s5670-i-mini.html">different types</a>. There are two types of arrays, it is numeric, which has numeric indexes (keys) and associative, with lowercase indices.</li> <li><b>An object</b>– Can be one of two data types, or <a href="https://zhumor.ru/en/internet/kak-sozdat-associativnyi-massiv-v-javascript-jquery---perebor-massiva-obekta-i.html">associative array</a>, or an instance of some class.</li> </ul><p>Variables can be used directly in a string. For example, let's create several variables of different types and display them all at once, in one line.</p> <p>I want to note that variables are always displayed without quotes.</p><p>Var age = 47; var money = 50.5; var name = "Ralph"; document.write(" <p>My name is <strong>" + name + "</strong>.<br />to me <strong>" + age + " years</strong> and i have <strong>" + money + " rubles</strong> </p>"); </p> <p> <br><img src='https://i1.wp.com/sozdatisite.ru/images/img-articles/ispolzovanie-peremennyx.jpg' width="100%" loading=lazy loading=lazy></p> <p><b>Boolean variables</b>(type Boolean) are rarely used directly in a string. They are more intended to store the result of various logical operations. Then this result is most often used for the conditional if statement, which we will study in another article.</p> <p>For example, after all, let's try to display them in the browser.</p> <p>Let's declare two boolean variables, one with a value of true and the other with a value of false. And we use them as answers to two questions.</p><p>bool_1 = true; var bool_2 = false; document.write(" <p><strong>Question:</strong> Do you want to become a programmer?</br > <strong>Answer:</strong>" + bool_1 + " (True)</p>"); document.write(" <p><strong>Question:</strong> Did the boy do his homework?</br > <strong>Answer:</strong>" + bool_2 + " (False)</p>"); </p><p>Save the document and open it in the browser.</p> <p> <img src='https://i1.wp.com/sozdatisite.ru/images/img-articles/bulevskie-peremennye.jpg' height="289" width="362" loading=lazy loading=lazy></p> <p>As you can see in JavaScript, the values ​​of boolean variables are displayed as they are set. In PHP they are displayed differently.</p> <p>You can declare a variable initially without assigning a value, then do it if necessary.</p><p>varmouse; //Some code mouse = "mouse";</p><p>You can also declare several variables at once, separated by commas, using the var keyword only once.</p><p>Var comp, television, auto; var count = 5, current_year = 2016, phone;</p><p>Arrays and objects are complex data types, so we will cover them in other articles.</p> <h2>Arithmetic operations</h2> <p>Now let's start with arithmetic operations. There are a couple of nuances that must be taken into account when writing code, otherwise you will get an incorrect result.</p> <p>First, let's declare two variables with arbitrary numeric values. Which we will use in operations.</p> <h3>Addition of variables</h3> <p>Let's start with the most common operation, addition.</p><p>Var x = - 8; vary = 14.7; //Insert the result of the addition into the result variable. varresult = x + y; document.write(x + " + " + y + " = " + result);</p><p>As a result, we will get such a number 6.699999999999999.</p> <p>Also, addition can be done immediately when deriving variables, but there is one important point here. In order to perform an arithmetic operation with numbers immediately upon their output, you need to do this inside parentheses. Otherwise, the numbers will be combined.</p> <p>We remove the result variable and try to add the variables immediately upon output.</p><p>Var x = - 8; vary = 14.7; //Insert the result of the addition into the result variable. document.write(" <p><strong<Верный результат (x + y):</strong< " + x + " + " + y + " = " + (x+y) + "</p>"); document.write(" <p><strong<Неверный результат x + y:</strong< " + x + " + " + y + " = " + x+y + "</p>"); </p><p>Save the document and look at the result:</p> <p> <br><img src='https://i1.wp.com/sozdatisite.ru/images/img-articles/slozhenie-peremennyx.png' width="100%" loading=lazy loading=lazy></p> <p>The correct result is obvious. Therefore, always, with any arithmetic operation, use parentheses.</p><p>Document.write(" <p>"+x+" - "+y+" = "+(x-y)+"</p>"); document.write(" <p>" + x +" * "+ y +" = "+ (x*y) + "</p>"); document.write(" <p>" + x +" / "+ y +" = "+ (x/y) + "</p> "); </p><p>And here is the result:</p> <p> <br><img src='https://i0.wp.com/sozdatisite.ru/images/img-articles/arifmeticheskie-operacii.png' width="100%" loading=lazy loading=lazy></p> <p>In programming, there is another important operator that you definitely met in the math lesson. It's about <b>operator "remainder of division", it is indicated by a percent sign (%)</b>.</p> <p>To better understand how this operator works, I will give a small example.</p><p>Var x = 20; vary = 6; document.write(" <p>" + x +" % "+ y +" = "+ (x%y) + "</p>"); //Result: 2</p><p>Why is 20% 6 equal to 2 ? Because 6 * 3 is equal to 18 and until 20 remains 2. That is, 2 is the remainder of the division of 20 / 6.</p> <p>This operator (%) is most often used in loops.</p> <h3>increment and decrement</h3> <p><b>Increment</b> is an increase in the value of a variable by one.</p> <p>For example, there is some variable x with value 1. And we want to increase the value of this variable by one. And instead of writing x = x + 1 like this, it's better to use an increment and write x++ like this, the result will be 2.</p><p>Var x = 1; x++; //Instead of x = x + 1. document.write(" x = " + x); //Result: x = 2.</p><p>You can also write ++x like this, the result will also be 2.</p><p>Var x = 1; ++x; //Instead of x = x + 1. document.write(" x = " + x); //Result: x = 2</p><p>If we make an increment immediately upon output, then in the case of ++x, the value will change, but in the case of x++, no, that is, the value will remain the same.</p> <p>The result remains the same.</p><p>Var x = 1; document.write(" x = " + (x++)); //Result: x = 1</p><p>The value will increase by 1.</p><p>Var x = 1; document.write(" x = " + (++x)); //Result: x = 2</p><p><b>Decrement</b>– This is the inverse of the increment operation. That is, decreasing the value of the variable by one.</p><p>Var x = 10; x--; //Instead of x = x - 1. document.write(" x = " + x); //Result: x = 9</p><p>All operations with an increment are similar to those with a decrement.</p> <h4>Difference between x++ and ++x</h4>var x = 5; vary; y = ++x; // y = 6, x = 6: first increment x by 1, then y = x. y = --x; // y = 5, x = 5: first decrease x by 1, then y = x. y=x++; // y = 5, x = 6: first set to y = x, then x incremented by 1. document.write(y); // y = 6 <p>The increment is always used in loops. The decrement is also used, but much less frequently.</p> <h4>Abbreviated notation for arithmetic operations</h4> <p>For all arithmetic operations, there is also an abbreviated notation. It is valid only when we want to perform some operation with only one variable. For example:</p> <ul><li>instead of x = x + 10; you can write x += 10;</li> <li>instead of x = x - 3; you can write x -= 3;</li> <li>instead of x = x * 5; you can write x *= 5;</li> <li>instead of x = x / 2; you can write x /= 2;</li> <li>instead of x = x % 3; you can write x %= 3;</li> </ul><h2>String operations</h2> <p>Let's say there are two variables with string values. For example, one will contain the word 'sha' and the other 'rik'. We want to combine these words to make the word 'balloon'. To do this, we use the addition operation.</p><p>var slog_1 = "sha"; var slog_2 = "rick"; var word = slog_1 + slog_2; document.write(word); //Result: ball</p><p>Now let's take a look at this case. We know that you can store both numbers and strings in a variable, but you can also store string numbers (for example, var = "64"). Let's say we have two such variables with string numbers and we need to add these numbers.</p> <p>If we just use the addition operation, we will get the wrong result, since the numbers will be combined, not added.</p><p>Var x = "78"; var y = "90"; document.write("result = "+ (x + y));//Result: result = 7890</p><p>Therefore, before doing any operation with string numbers, you must first convert them from a string to a number. This is done using the function <b>Number()</b>.</p><p>Var x = "78"; var y = "90"; x = Number(x); y = number(y); document.write("result = "+ (x + y));//Result: result = 168</p><h2></h2> <p>Now let's start with logical operations. Only boolean data is used here, true (true) and false (false).</p> <p>For example, after comparing two numbers, we get some boolean result, either true or false.</p><p>var count_ball = 16, count_players = 32, compare; compare = count_ball > count_players; document.write(count_ball + " > " + count_players + " = " + compare + " <br />"); //false compare = count_ball< count_players; document.write(count_ball + " < " + count_players + " = " + compare + "<br />"); //true</p><p>These operations are most often used in if, else conditional statements.</p> <p>For a better understanding, I will show you the truth table. You must know it by heart. To do this, it is enough to understand it.</p> <p> <br><img src='https://i2.wp.com/sozdatisite.ru/images/img-articles/tablica-istinnosti.png' width="100%" loading=lazy loading=lazy></p> <p><b>Instead of true it can be 1, and instead of false 0.</b></p> <p><b>&& - This is the AND operator, i.e. AND.</b> It can be understood as a multiplication operator.</p> <ul><li>0(false) && 0(false) = 0(false)</li> <li>0(false) && 1(true) = 0(false)</li> <li>1(true) && 0(false) = 0(false)</li> <li>1(true) && 1(true) = 1(true)</li> </ul><p><b>|| - This is an OR operator, that is, OR.</b> It can be understood as an addition operator.</p> <ul><li>0(false) || 0(false) = 0(false)</li> <li>0(false) || 1(true) = 1(true)</li> <li>1(true) || 0(false) = 1(true)</li> <li>1(true) || 1(true) = 1(true)</li> </ul><p>Symbol "|" on the keyboard is typed using the combination <a href="https://zhumor.ru/en/internet/chto-delat-esli-ne-rabotaet-klavisha-shift-ne-rabotaet-shift-na-klaviature.html">Shift keys</a>+ Back slesh(Back slash \).</p> <p><b>^ - This is the XOR operator, i.e. Exclusive OR.</b> It is rarely used. But you need to know it for anyone, suddenly you need it.</p> <ul><li>0(false) ^ 0(false) = 0(false)</li> <li>0(false) ^ 1(true) = 1(true)</li> <li>1(true) ^ 0(false) = 1(true)</li> <li>1(true) ^ 1(true) = 0(false)</li> </ul><p>That's all I wanted to tell you about in this article. Now you know what types of variables exist in programming and how to use them in various arithmetic and logical operations.</p> <script>document.write("<img style='display:none;' src='//counter.yadro.ru/hit;artfast?t44.1;r"+ escape(document.referrer)+((typeof(screen)=="undefined")?"": ";s"+screen.width+"*"+screen.height+"*"+(screen.colorDepth? screen.colorDepth:screen.pixelDepth))+";u"+escape(document.URL)+";h"+escape(document.title.substring(0,150))+ ";"+Math.random()+ "border='0' width='1' height='1' loading=lazy loading=lazy>");</script> <div class="clear"></div> <div class="share"> <div class="title">Liked the article? 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