javascript reads like this

JavaScript is pronounced like this

JavaScript, the Chinese name is "JavaScript scripting language", is a programming language that runs on the browser side. It is the core language for developing interactive web pages. It is widely used in web page production, web page special effects, web application development and other fields. It is considered one of the "Troika of the World Wide Web".

The learning and mastering of JavaScript is very important for programmers engaged in web development. In this article, we will introduce the basic knowledge, grammatical rules and common usage of JavaScript to help beginners better understand and master JavaScript.

1. Basic knowledge of JavaScript

1. History

JavaScript originated in 1995 and was originally developed by Brendan Eich, a programmer at Netscape. It was called "LiveScript" at the time and was later renamed JavaScript. In 1996, because JavaScript was somewhat related to Sun's Java, Netscape submitted it to ECMA (European Computer Manufacturers Association) and released the ECMAScript standard. JavaScript is widely used as an implementation of ECMAScript.

2. Features

JavaScript is an "interpreted" language that does not require a compiler to run. It implements multiple programming paradigms, including object-oriented programming, functional programming, and imperative programming. Compared with other programming languages, JavaScript has the following characteristics:

①Dynamicity: JavaScript supports dynamic types and also supports dynamic code generation.

②Flexibility: JavaScript supports event drive and can add interactive effects to web pages.

③ Close integration with HTML: JavaScript can be embedded in HTML pages and run directly in the browser.

④Cross-platform: JavaScript can run in multiple operating systems and can also span multiple browser platforms.

3. Function

JavaScript can realize interactive effects, form verification, dynamic style modification, DOM operations and other functions in web pages. At the same time, JavaScript can also interact with the server through Ajax technology to achieve asynchronous loading and dynamic refresh of data.

4. Development environment

JavaScript is a lightweight language that does not require a special development environment, only a text editor and browser. Common text editors include Notepad, Sublime Text, Visual Studio Code, etc. As for the browser, you can choose Chrome, Firefox, IE, etc.

2. JavaScript syntax rules

1. Comments

Comments can be added to JavaScript code to make it easier for others to read and understand the code. JavaScript supports single-line comments and multi-line comments, as shown below:

Single-line comment: //This is a single-line comment

Multi-line comment:
/*
This is a multi-line comment
can contain multiple lines of content
*/

2. Variables

JavaScript variables must be declared before use, use the var key The variable is declared as follows:

var num = 10;//A variable named num is declared, with an initial value of 10

3. Data type

JavaScript data types include: strings, numbers, Boolean values, arrays, objects, Null and Undefined. The string must be enclosed in quotation marks, the number can be an integer or a floating point number, and the Boolean value has only two values: true and false.

4. Control statements

JavaScript control statements include: if statement, for statement, while statement, switch statement, etc. The if statement is used to determine whether a condition is met, the for statement is used to execute a piece of code in a loop, the while statement is used to loop a piece of code until the condition is not met, and the switch statement is used to execute different code blocks based on different conditions.

5. Function

A JavaScript function can be understood as a piece of reusable code, defined with the function keyword. A function can accept parameters and return a value as follows:

function add(a, b){
return a b;
}
var result = add(3, 4) ;//Call the add function and assign the return value to the result variable

6. Object

JavaScript objects are entities composed of attributes and methods. "Attributes" refer to Represents the state of the object, while "method" refers to the behavior of the object. Objects can be represented by curly braces {}, as shown below:

var person = {

name:"Tom",
age:20,
sayHello:function(){
    console.log("Hello, my name is " + this.name);
}

};
person.sayHello();//Call person’s sayHello method and output “Hello, my name is Tom”

3. Common usage

1. Event binding

JavaScript can bind events to HTML elements and trigger different The response function is as follows:

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In this example, when the user clicks When the button is pressed, a warning box pops up and displays "Hello World".

2. Dynamic style control

You can dynamically control the style of elements through JavaScript, as shown below:

var element = document.getElementById("myDiv" );
element.style.color = "red";

In this example, first get the element with the id "myDiv" in the page, and then set its text color to red.

3. DOM operation

JavaScript can operate DOM (Document Object Model) nodes in web pages, that is, you can add, modify, and delete HTML elements and attributes. As shown below:

var newelement = document.createElement("p");//Create a new e388a4556c0f65e1904146cc1a846bee element
var textnode = document.createTextNode("This is new.");/ /Create a text node
newelement.appendChild(textnode);//Add the text node to the e388a4556c0f65e1904146cc1a846bee element
document.getElementById("myDiv").appendChild(newelement);//Add c852e9f44254fc96ef7cc6d3d1da32e1 element is added to the element with the id "myDiv"

In this example, first create a new e388a4556c0f65e1904146cc1a846bee element and add a text node, then add the e388a4556c0f65e1904146cc1a846bee element to In the element with the id "myDiv" on the page.

Conclusion

This article introduces the basic knowledge, grammatical rules and common usage of JavaScript. For beginners, it is very important to master these basic knowledge. At the same time, it is recommended that beginners start with simple examples, gradually understand the syntax and characteristics of JavaScript in depth, and continue to practice and try in order to better master this language.

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