JavaScript Introduction

JavaScript is the most popular programming language in the world.

This page contains some examples of what JavaScript can do.

JavaScript Can Change HTML Content

One of many HTML methods is getElementById().

This example uses the method to "find" an HTML element (with id="demo"), and changes the element content (innerHTML) to "Hello JavaScript":


document.getElementById("demo").innerHTML = "Hello JavaScript";
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JavaScript Can Change HTML Attributes

This example changes an HTML image, by changing the src attribute of an <img> tag:

The Light bulb

Click the light bulb to turn on/off the light

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JavaScript Can Change HTML Styles (CSS)

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


document.getElementById("demo").style.fontSize = "25px";
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JavaScript Can Validate Data

JavaScript is often used to validate input:

Please input a number between 1 and 10

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Did You Know?

Note JavaScript and Java are completely different languages, both in concept and design.
ECMA-262 is the official name. ECMAScript 6 (released in June 2015) is the latest official version of JavaScript.