JavaScript Introduction

JavaScript is the programming language of the web.

What Can JavaScript Do?

JavaScript is the programming language of the web.

It can calculate, manipulate and validate data.

It can update and change both HTML and CSS.

JavaScript Can Change HTML Content

One of many JavaScript HTML methods is getElementById().

The example below "finds" an HTML element (with id="demo"), and changes the element content (innerHTML) to "Hello JavaScript":

Example

Example Code

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document.getElementById("demo").innerHTML = "Hello JavaScript";

JavaScript accepts both double and single quotes:

Example

Example Code

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document.getElementById('demo').innerHTML = 'Hello JavaScript';

JavaScript Can Change HTML Attribute Values

In this example JavaScript changes the value of the src (source) attribute of an tag:

JavaScript Can Change HTML Styles (CSS)

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

Example

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document.getElementById("demo").style.fontSize = "35px";

JavaScript Can Hide HTML Elements

Hiding HTML elements can be done by changing the display style:

Example

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document.getElementById("demo").style.display = "none";

JavaScript Can Show HTML Elements

Showing hidden HTML elements can also be done by changing the display style:

Example

Example Code

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document.getElementById("demo").style.display = "block";

Did You Know? > JavaScript and Java are two 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 of the standard. ECMAScript is the official name of the language. > See all JavaScript Versions