What is the use of variables in javascript

In JavaScript, a variable is a container that temporarily stores values. It can be used to store data, and the contents of the variable can be set, updated, or read when needed. Using variables can give a short and easy-to-remember name for a piece of data to be used in the program, and can also save data entered by the user or the results of operations.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

Variables are one of the foundations of all programming languages. They can be used to store data, such as strings, numbers, Boolean values, arrays, etc., and set, update or read the contents of the variables when needed.

The value of a variable will change at any time during the running of the program. It can give a short and easy-to-remember name for a piece of data to be used in the program. In addition, it can also save the data input by the user or the result of the operation.

Define variables

In JavaScript, you need to use the var keyword to define variables. The syntax is as follows:

var 变量名;

A few examples:

var str;  //用来存储字符串
var age;  //用来存储年龄
var prePage;  //用来存储上一页

When defining variables, you can define one or more variables at a time. If you define multiple variables, you need to use commas between variable names to separate them, as shown in the following example:

var a, b, c;    // 同时声明多个变量

After the variables are defined, if no values ​​are assigned to the variables, then these variables will be assigned an initial value - undefined (undefined).

Naming rules for variables

In JavaScript, variable names cannot be defined casually and need to follow the naming rules for identifiers, as follows:

• Variable names can contain numbers, letters, underscores _, and dollar signs $;

• Chinese characters cannot appear in variable names;

• Variable names cannot contain spaces;

• Variable names cannot be keywords or reserved words in JavaScript;

• Variable names It cannot start with a number, that is, the first character cannot be a number.

When defining a variable, the variable name should be as meaningful as possible so that you or others can easily understand it. For example, you can use name to define a variable that stores names, and dataArr to define a variable that stores names. Variable of array type.

When the variable name contains multiple English words, it is recommended to use camel case naming (big camel case: the first letter of each word is capitalized, such as FileType, DataArr; small camel case: the first letter of the first word is lowercase and the following Capitalize the first letter of a word, such as fileType, dataArr).

Assign a value to the variable

After the variable is defined, you can use the equal sign = to assign a value to the variable. The left side of the equal sign is the name of the variable. The right side of the equal sign is the value to be assigned to the variable, as shown in the following example:

var num;    // 定义一个变量 num
num = 1;    // 将变量 num 赋值为 1

In addition, you can also assign a value to the variable while defining the variable, as shown in the following example:

var num = 1;                // 定义一个变量 num 并将其赋值为 1
var a = 2, b = 3, c = 4;    // 同时定义 a、b、c 三个变量并分别赋值为 2、3、4
// var a = 2,               // 为了让代码看起来更工整，上一行代码也可以写成这样
//     b = 3,
//     c = 4;

[Recommended learning ：javascript advanced tutorial】

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