“I am delighted to support Nicolás’ endeavor because his book looks exactly like what people who are coming to JavaScript with fresh eyes need.”
– Brendan Eich
Ideal for professional software developers with a basic understanding of JavaScript, this practical book shows you how to build small, interconnected ES6 JavaScript modules that emphasize reusability. You’ll learn how to face a project with a modular mindset, and how to organize your applications into simple pieces that work well in isolation and can be combined to create a large, robust application.
This book focuses on two aspects of JavaScript development: modularity and ES6 features. You’ll learn how to tackle application development by following a scale-out approach. As pieces of your codebase grow too big, you can break them up into smaller modules.
The book can be read online for free or purchased through Amazon.
This book is part of the Modular JavaScript series.
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Chapter 1
ECMAScript and the Future of JavaScript
JavaScript has gone from being a 1995 marketing ploy to gain a tactical advantage to becoming the core programming experience in the world’s most widely used application runtime platform in 2017. The language doesn’t merely run in browsers anymore, but is also used to create desktop and mobile applications, in hardware devices, and even in space suit design at NASA.
How did JavaScript get here, and where is it going next?
A Brief History of JavaScript Standards
Back in 1995, Netscape envisioned a dynamic web beyond what HTML could offer. Brendan Eich was initially brought into Netscape to develop a language that was functionally akin to Scheme, but for the browser. Once he joined, he learned that upper management wanted it to look like Java, and a deal to that effect was already underway.
Brendan created the first JavaScript prototype in 10 days, taking Scheme’s first-class functions and Self’s prototypes as its main ingredients. The initial version of JavaScript was code-named Mocha. It didn’t have array or object literals, and every error resulted in an alert. The lack of exception handling is why, to this day, many operations result in NaN or undefined. Brendan’s work on DOM level 0 and the first edition of JavaScript set the stage for standards work.
This revision of JavaScript was marketed as LiveScript when it started shipping with a beta release of Netscape Navigator 2.0, in September 1995. It was rebranded as JavaScript (trademarked by Sun, now owned by Oracle) when Navigator 2.0 beta 3 was released in December 1995. Soon after this release, Netscape introduced a server-side JavaScript implementation for scripting in Netscape Enterprise Server, and named it LiveWire.1 JScript, Microsoft’s reverse-engineered implementation of JavaScript, was bundled with IE3 in 1996. JScript was available for Internet Information Server (IIS) in the server side.
The language started being standardized under the ECMAScript name (ES) into the ECMA-262 specification in 1996, under a technical committee at ECMA known as TC39. Sun wouldn’t transfer ownership of the JavaScript trademark to ECMA, and while Microsoft offered JScript, other member companies didn’t want to use that name, so ECMAScript stuck.
Disputes by competing implementations, JavaScript by Netscape and JScript by Microsoft, dominated most of the TC39 standards committee meetings at the time. Even so, the committee was already bearing fruit: backward compatibility was established as a golden rule, bringing about strict equality operators (=== and !==) instead of breaking existing programs that relied on the loose Equality Comparison Algorithm.
The first edition of ECMA-262 was released June 1997. A year later, in June 1998, the specification was refined under the ISO/IEC 16262 international standard, after much scrutiny from national ISO bodies, and formalized as the second edition.
By December 1999 the third edition was published, standardizing regular expressions, the switch statement, do/while, try/catch, and Object#hasOwnProperty, among a few other changes. Most of these features were already available in the wild through Netscape’s JavaScript runtime, SpiderMonkey.
Drafts for an ES4 specification were soon afterwards published by TC39. This early work on ES4 led to JScript.NET in mid-20002 and, eventually, to ActionScript 3 for Flash in 2006.3
Conflicting opinions on how JavaScript was to move forward brought work on the specification to a standstill. This was a delicate time for web standards: Microsoft had all but monopolized the web and they had little interest in standards development.
As AOL laid off 50 Netscape employees in 2003,4 the Mozilla Foundation was formed. With over 95% of web-browsing market share now in the hands of Microsoft, TC39 was disbanded.
It took two years until Brendan, now at Mozilla, had ECMA resurrect work on TC39 by using Firefox’s growing market share as leverage to get Microsoft back in the fold. By mid-2005, TC39 started meeting regularly once again. As for ES4, there were plans for introducing a module system, classes, iterators, generators, destructuring, type annotations, proper tail calls, algebraic typing, and an assortment of other features. Due to how ambitious the project was, work on ES4 was repeatedly delayed.
By 2007 the committee was split in two: ES3.1, which hailed a more incremental approach to ES3; and ES4, which was overdesigned and underspecified. It wouldn’t be until August 20085 when ES3.1 was agreed upon as the way forward, but later rebranded as ES5. Although ES4 would be abandoned, many of its features eventually made its way into ES6 (which was dubbed Harmony at the time of this resolution), while some of them still remain under consideration and a few others have been abandoned, rejected, or withdrawn. The ES3.1 update served as the foundation on top of which the ES4 specification could be laid in bits and pieces.
In December 2009, on the 10-year anniversary since the publication of ES3, the fifth edition of ECMAScript was published. This edition codified de facto extensions to the language specification that had become common among browser implementations, adding get and set accessors, functional improvements to the Array prototype, reflection and introspection, as well as native support for JSON parsing and strict mode.
A couple of years later, in June 2011, the specification was once again reviewed and edited to become the third edition of the international standard ISO/IEC 16262:2011, and formalized under ECMAScript 5.1.
It took TC39 another four years to formalize ECMAScript 6, in June 2015. The sixth edition is the largest update to the language that made its way into publication, implementing many of the ES4 proposals that were deferred as part of the Harmony resolution. Throughout this book, we’ll be exploring ES6 in depth.
In parallel with the ES6 effort, in 2012 the WHATWG (a standards body interested in pushing the web forward) set out to document the differences between ES5.1 and browser implementations, in terms of compatibility and interoperability requirements. The task force standardized String#substr, which was previously unspecified; unified several methods for wrapping strings in HTML tags, which were inconsistent across browsers; and documented Object.prototype properties like __proto__ and __defineGetter__, among other improvements.6 This effort was condensed into a separate Web ECMAScript specification, which eventually made its way into Annex B in 2015. Annex B was an informative section of the core ECMAScript specification, meaning implementations weren’t required to follow its suggestions. Jointly with this update, Annex B was also made normative and required for web browsers.
The sixth edition is a significant milestone in the history of JavaScript. Besides the dozens of new features, ES6 marks a key inflection point where ECMAScript would become a rolling standard.
