[JavaScript Tutorial] Introduction to JavaScript

Introduction to JavaScript

JavaScript is the most popular scripting language on the Internet. This language can be used for HTML and web, and can be widely used on servers, PCs, laptops, tablets, smartphones and other devices.

JavaScript is a scripting language

JavaScript is a lightweight programming language.

JavaScript is programming code that can be inserted into HTML pages.

JavaScript, when inserted into an HTML page, can be executed by all modern browsers.

JavaScript is easy to learn.

What you will learn

Here are the main things you will learn in this tutorial.

JavaScript: Write directly to HTML output stream

Example

document.write("<h1>这是一个标题</h1>");
document.write("<p>这是一个段落。</p>");

You can only use document.write with HTML output. If you use this method after the document is loaded, the entire document will be overwritten.

JavaScript: Reaction to events

Example

<button type="button" onclick="alert(&#39;欢迎!&#39;)">点我!</button>

alert() function is not commonly used in JavaScript, but it is very convenient for code testing. The

onclick event is just one of many events you are about to learn about in this tutorial.

JavaScript: Change HTML content

Using JavaScript to process HTML content is a very powerful feature.

Example

x=document.getElementById("demo")  //查找元素
x.innerHTML="Hello JavaScript";    //改变内容

You will often see document.getElementById("some id"). This method is defined in the HTML DOM.

DOM (Document Object Model) is the official W3C standard for accessing HTML elements.

You will learn about HTML DOM in multiple chapters of this tutorial.

JavaScript: Change HTML image

This example will dynamically change the source (src) of HTML :

Light up the light bulb

JavaScript can change most attributes of any HTML element, not just images.

JavaScript: Change HTML style

Change the style of HTML elements, which is a variant of changing HTML attributes.

Example

x=document.getElementById("demo")  //找到元素 
x.style.color="#ff0000";           //改变样式

JavaScript: Validating input

JavaScript is often used to validate user input.

Example

if isNaN(x) {alert("不是数字")};

Did you know?

JavaScript and Java are two completely different languages, both in concept and design.
Java (invented by Sun) is a more complex programming language.

ECMA-262 is the official name of the JavaScript standard.

JavaScript was invented by Brendan Eich. It appeared in Netscape in 1995 (the browser is no longer being updated) and was adopted by ECMA (a standards association) in 1997.

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