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How to write javascript js file

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May 16, 2023 am 09:10 AM

JavaScript is a powerful programming language that can implement functions such as interaction, dynamic effects, and data manipulation on web pages. JS files are the storage carrier of JavaScript code. This article will introduce how to write JS files.

1. Creation of JS files

JS files can be created using any text editor or JS development tool, such as Notepad, Sublime Text, Visual Studio Code, etc. To create a JS file, just create a new blank text file and end the file name with .js, such as "index.js", "script.js", etc.

2. The basic structure of JS files

The basic structure of JS files consists of the following parts:

1. Comments
Comments are important in JS code It can help us better understand the function and logic of the code, and facilitate later maintenance and modification. Comments can use "//" or "/ /", the former represents a single-line comment, and the latter represents a multi-line comment.

2. Function declaration
Function is the basic unit of JS code. It can encapsulate a set of JavaScript statements together to form a reusable block to achieve code reuse and modular development. Function declarations can be created using the "function" keyword and adding the function parameters and function body in parentheses.

3. Variable declaration
Variables are memories in JS code. They are used to store various types of data, including numbers, strings, objects, etc. Variable declarations can be created using the "var", "let" or "const" keywords and appending the value after the variable name.

The following is the basic structure of a JS file:

//此处为单行注释
/*
此处为多行注释
*/

//函数声明
function functionName(parameter1, parameter2) {
   //函数体
}

//变量声明
var variableName = value;
let variableName = value;
const variableName = value;

3. Code examples in JS files

The following are code examples in some JS files, which demonstrate JS Common uses of files:

1. Change the background color of an element to red:

document.getElementById("element_id").style.backgroundColor = "red";

2. Create an array:

let myArray = [1, 2, 3, 4, 5];

3. Declare a variable and assign it to String:

let myString = "Hello, World!";

4. Loop through the array elements and print:

for (let i = 0; i < myArray.length; i++) {
   console.log(myArray[i]);
}

4. How to introduce JS files

JS files can be introduced in the following three ways:

1. Internal JS
Use the "script" tag in the HTML file to introduce the JS file. The tag can be placed at the head or tail of the HTML file, as shown below:

<!DOCTYPE html>
<html>
<head>
   <title>My Page</title>
   <script type="text/javascript" src="my_script.js"></script>
</head>
<body>
<!-- HTML 页面内容 -->
</body>
</html>

2. External JS
Introducing external JS files into HTML files, you can use absolute or relative path references, as shown below:

<script type="text/javascript" src="https://example.com/my_script.js"></script>

<script type="text/javascript" src="/js/my_script.js"></script>

3. Inline JS
Use onload, onclick in HTML files Bind attributes to other events and introduce JS code, as shown below:

<button onclick="myFunction()">Click me</button>

The above is the creation, basic structure, code examples and introduction methods of JS files. I hope this article can help you better understand JavaScript programming and JS How to write files.

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