JavaScript Introduction

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JavaScript is the world's most popular programming language.

It is the language for HTML, for the web, for servers, PCs, laptops, tablets, phones, and more.

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JavaScript is a Scripting Language

A scripting language is a lightweight programming language.

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

JavaScript code can be executed by all modern web browsers.

JavaScript is easy to learn.

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What You Will Learn

Below is a taste of what you will learn in this tutorial.

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JavaScript: Writing Into HTML Output

Example

document.write("<h1>This is a heading</h1>");
document.write("<p>This is a paragraph</p>");

	You can only use document.write in the HTML output. If you use it after the document has loaded, the whole document will be overwritten.

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JavaScript: Reacting to Events

Example

<button type="button" onclick="alert('Welcome!')">Click Me!</button>

The alert() function is not much used in JavaScript, but it is quite handy for trying out code.

The onclick event is only one of the many HTML events you will learn about in this tutorial.

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JavaScript: Changing HTML Content

Using JavaScript to manipulate the content of HTML elements is a very common.

Example

x=document.getElementById("demo")  //Find the element
x.innerHTML="Hello JavaScript";    //Change the content

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

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

You will find several chapters about the HTML DOM in this tutorial.

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JavaScript: Changing HTML Images

This example dynamically changes the source (src) attribute of an HTML <image> element:

The Light bulb

Click the light bulb to turn on/off the light

With JavaScript, you can change almost any HTML attribute.

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JavaScript: Changing HTML Styles

Changing the style of an HTML element, is a variant of changing an HTML attribute.

Example

x=document.getElementById("demo")  //Find the element
x.style.color="#ff0000";           //Change the style

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JavaScript: Validate Input

JavaScript is commonly used to validate input.

Example

if isNaN(x) {alert("Not Numeric")};

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Did You Know?

JavaScript and Java are two completely different languages, in both concept and design. Java (invented by Sun) is a more complex programming language in the same category as C. ECMA-262 is the official name of the JavaScript standard. JavaScript was invented by Brendan Eich. It appeared in Netscape (a no longer existing browser) in 1995, and has been adopted by ECMA (a standard association) since 1997.