Professional JavaScript for Web Developers, 4th Edition

INTRODUCTION

A tech lead at Google once shared with me a compelling perspective on JavaScript: It's not really a cohesive programming language—at least not in the formal sense. The ECMA-262 specification defines JavaScript, but there is no single true implementation of it. What's more, the language is far from hermetic. It swims in a veritable ocean of adjacent specifications that govern APIs for everything that JavaScript touches: the DOM, network requests, system hardware, storage, events, files, cryptography, and hundreds of others. Web browsers and their various JavaScript engines all implement these specifications as they see fit. Chrome has Blink/V8, Firefox has Gecko/SpiderMoney, and Safari has WebKit/JavaScriptCore. Browsers will run nearly all JavaScript in a way that conforms to the specifications, but the web is littered with examples of each browser's idiosyncrasies. Therefore, JavaScript is more accurately characterized as a constellation of browser implementations.

Although web purists might insist that JavaScript should not be an integral component of web pages, they must concede that the modern web is severely diminished without it. It is not hyperbolic to say that JavaScript is virtually inescapable: Phones, computers, tablets, televisions, game consoles, smart watches, refrigerators, and even cars now feature web browsers that run JavaScript. Nearly three billion people now use a smartphone that includes a web browser. The language's vibrant community churns ...