Professional JavaScript for Web Developers, 5th Edition

INTRODUCTION

A tech lead at Google once shared with me a compelling perspective on JavaScript: It's not really a programming language. The ECMA-262 specification defines JavaScript, but there is no single true implementation of it. Web browsers and their JavaScript engines all implement this specification as they see fit. Chrome has Blink/V8, Firefox has Gecko/SpiderMonkey, and Safari has WebKit/JavaScriptCore. What's more, the language swims in an ocean of supplementary specifications that govern APIs for everything that JavaScript touches: the DOM, network requests, system hardware, storage, events, files, cryptography, and hundreds of others. Therefore, JavaScript is more accurately characterized as a constellation of ECMAScript implementations buttressed by an API buffet.

The first edition of this book was published in 2005. Microsoft was still pushing its rogue JScript, Internet Explorer had over a 90 percent browser market share, mobile browsers were in the Stone Age, and jQuery wouldn't be released for another year. At the time this fifth edition was written in 2023, major browsers have coalesced around the ECMA-262 specification, over 70 percent of Internet traffic uses a Chromium-based browser, mobile browser traffic exceeds desktop traffic, and modern web development largely comprises manipulating frameworks like React and Angular.

Most web developers would identify the release of ECMAScript 6 as JavaScript's Cambrian explosion. Pre-ES6, the language advanced in infrequent ...