# JavaScript Introduction

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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 document.getElementById().

This example "finds" the HTML element with id="demo", and changes its content (innerHTML):

## Example

document.getElementById("demo").innerHTML = "Hello JavaScript";
Try it Yourself »

## 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

Try it Yourself »

## JavaScript Can Change HTML Styles (CSS)

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

## Example

document.getElementById("demo").style.fontSize = "25px";
Try it Yourself »

## JavaScript Can Validate Data

JavaScript is often used to validate input:

Please input a number between 1 and 10

Try it Yourself »

## Did You Know?

| JavaScript and Java are completely different languages, both in concept and design. JavaScript was invented by Brendan Eich in 1995, and became an ECMA standard in 1997. ECMA-262 is the official name. ECMAScript 5 (JavaScript 1.8.5 - July 2010) is the latest standard.

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