JavaScript data types

JavaScript data types have the following types

String
Number
Boolean
Array
Object(Object)
Null
Undefined.

JavaScript has dynamic typing

JavaScript has dynamic typing. This means that the same variable can be used as different types, like this

var x; var x = "John"; // Now x is a string

JavaScript string
Strings are variables that store characters (such as "Bill Gates").

The string can be any text in quotes. You can use single or double quotes:

var carname="Volvo XC60";
var carname='Volvo XC60';
You can use quotes within a string as long as it does not match the quotes surrounding the string:

Example

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>PHP中文网(PHP.CN)</title>
</head>
<body>
<script>
    var carname1="我是双引号";
    var carname2='我是单引号';
    var answer1="这是正常的";
    var answer2="我的名字是 'Johnny'";
    var answer3='我的名字是 "Johnny"';
    document.write(carname1 + "<br>")
    document.write(carname2 + "<br>")
    document.write(answer1 + "<br>")
    document.write(answer2 + "<br>")
    document.write(answer3 + "<br>")
</script>
</body>
</html>

Run the code Try it

JavaScript NumbersJavaScript has only one number type. Numbers can be with or without a decimal point:

var x1=34.00; //Use decimal point to write
var x2=34; // //Do not use decimal point to write

very large or very small numbers It can be written in scientific (exponential) notation:

Example

<!DOCTYPE html>
<html>
<head> 
<meta charset="utf-8"> 
<title>PHP中文网（php.cn）</title> 
</head>
<body>
<script>
var x1=34.00;
var x2=34;
var y=123e5;
var z=123e-5;
document.write(x1 + "<br>")
document.write(x2 + "<br>")
document.write(y + "<br>")
document.write(z + "<br>")
</script>
</body>
</html>

Run the program to try it

JavaScript Boolean

Boolean (logical) can only have two values: true or false.

var x=true;
var y=false;

JavaScript Array

The following code creates an array named cars:

var cars=new Array();
cars[0]="Saab";
cars [1]="Volvo";
cars[2]="BMW";

or (condensed array):

var cars=new Array( "Saab","Volvo","BMW");

or (literal array):

Example

<!DOCTYPE html>
<html>
<body>
<script>
    var i;
    var cars = new Array();
    cars[0] = "Saab";
    cars[1] = "Volvo";
    cars[2] = "BMW";
    for (i=0;i<cars.length;i++)
    {
        document.write(cars[i] + "<br>");
    }
</script>
</body>
</html>

Run the program and try it

Tips: Array subscripts are zero-based, so the first item is [0] and the second is [1], so analogy.

JavaScript Objects

Objects are separated by curly braces. Inside the brackets, the object's properties are defined as name and value pairs (name : value). Properties are separated by commas:

var person={firstname:"John", lastname:"Doe", id:5566};

Object in the above example ( person) has three attributes: firstname, lastname and id.

Spaces and line breaks don't matter. The statement can span multiple lines:

var person={
firstname : "John",
lastname : "Doe",
id : 5566
};

Object properties have two addressing methods:

<!DOCTYPE html>
<html>
<head> 
<meta charset="utf-8"> 
<title>php中文网(php.cn)</title> 
</head>
<body>
<script>
var person=
{
firstname : "John",
lastname  : "Doe",
id        :  5566
};
document.write(person.lastname + "<br>");
document.write(person["lastname"] + "<br>");
</script>
</body>
</html>

Run the program to try it

Undefined and Null

Undefined This value indicates that the variable does not contain a value.

You can clear a variable by setting its value to null.

<!DOCTYPE html>
<html>
<head> 
<meta charset="utf-8"> 
<title>php中文网(php.cn)</title> 
</head>
<body>
<script>
var person;
var car="Volvo";
document.write(person + "<br>");
document.write(car + "<br>");
var car=null
document.write(car + "<br>");
</script>
</body>
</html>

Run the program to try it out

Declaring variable types

When you declare a new variable, you can use Keyword "new" to declare its type:

var carname=new String;
var x= new Number;
var y= new Boolean;
var cars= new Array;
var person= new Object;

Tips: JavaScript variables are all objects. When you declare a variable, you create a new object.

Continuing Learning

new file

<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>PHP中文网(PHP.CN)</title> </head> <body> <script> var carname1="我是双引号"; var carname2='我是单引号'; var answer1="这是正常的"; var answer2="我的名字是 'Johnny'"; var answer3='我的名字是 "Johnny"'; document.write(carname1 + "<br>") document.write(carname2 + "<br>") document.write(answer1 + "<br>") document.write(answer2 + "<br>") document.write(answer3 + "<br>") </script> </body> </html>

submit Reset Code

Automatic operation

JavaScript data types

ElementaryImperial CMS enterprise imitation website tutorial

ElementaryNewbies with zero foundation in WordPress build personal blogs and corporate websites

ElementaryUltimate CMS zero-based website building instruction video

ElementaryFront-end project-Shangyou [HTML/CSS/JS technology comprehensive practice]

IntermediateVue3.0 from 0 to build a universal backend management system project practice

ElementaryZero-based front-end course [Vue advanced learning and practical application]

ElementaryWEB front-end tutorial [HTML5+CSS3+JS]

ElementaryQuick introduction to apipost

IntermediateVue3+TypeScript practical tutorial-enterprise-level project practice

ElementaryLet's briefly talk about starting a business in PHP

IntermediateVUE e-commerce project (front-end & back-end dual project actual combat)

ElementaryApipost practical application [api, interface, automated testing, mock]