JavaScript

Last Updated: 12/14/2022

Introduction

  • JavaScript is the one of the most popular programming language.
  • JavaScript and Java are completely different languages, both in concept and design.
  • HTML is used to define the content of web pages
  • CSS is used to specify the layout of web pages
  • JavaScript is used to program the behavior of web pages

ECMAScript

  • ECMAScript is a JavaScript standard/specification intended to ensure the interoperability of web pages across different browsers.
  • It is standardized by ECMA International

Versions

  • The Original JavaScript ES1 ES2 ES3 (1997-1999)
  • The First Main Revision ES5 (2009)
  • The Second Revision ES6 (2015)
  • Yearly Revision from 2016

Internal JavaScript

  • Scripts can be placed in the <body>, or in the <head> section of an HTML page, or in both.
  • Placing scripts at the bottom of the <body> element improves the display speed, because script interpretation slows down the display.
    • Old JavaScript examples may use a type attribute: <script type="text/javascript">. The type attribute is not required.
  • JavaScript is the default scripting language in HTML.
  • JavaScript code is inserted between <script> and </script> tags.

External JavaScript

  • Scripts can also be placed in external files
  • External scripts cannot contain <script> tags.
  • JavaScript files have the file extension .js.
  • It separates HTML and code
  • It makes HTML and JavaScript easier to read and maintain
  • Cached JavaScript files can speed up page loads.

<script src="index.js"></script>

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