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JavaScript Introduction


JavaScript is the most popular programming language in the world.

This page contains some examples of what JavaScript can do in HTML.


JavaScript Can Change HTML

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

Using the DOM, JavaScript can change and manipulate HTML.

You can use JavaScript to:

  • Change HTML content
  • Change HTML attributes
  • Change HTML styles
  • And much more ...

There are several chapters, about accessing the HTML DOM, later in this tutorial.


JavaScript Can Change HTML Content

One of many methods in the DOM is document.getElementById().

The following example "finds" the 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 the source of 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?

Note 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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