What Is JavaScript
Nicholas C. Zakas · 2015
This chapter provides information on review of JavaScript history, what JavaScript is, how JavaScript and ECMAScript are related, and finally the different versions of JavaScript. JavaScript is a scripting language designed to interact with web pages. It is made up of three distinct implementations: ECMAScript, the Document Object Model (DOM), and the Browser Object Model (BOM). The ECMAScript is defined in ECMA-262 and provides the core functionality. DOM provides methods and interfaces for working with the content of a web page. BOM provides methods and interfaces for interacting with the browser. Across the five major web browsers, Internet Explorer, Firefox, Chrome, Safari, and Opera, there are varying levels of support for the three parts of JavaScript. Support for ECMAScript 3 is generally good across all browsers, and support for ECMAScript 5 is growing, whereas support for the DOM varies widely.