JavaScript

The New Toys

T. J. Crowder

• Editore: Wrox
• Anno: 2020
• ISBN:
  9781119367963
• Edizione: 1
• Argomento: Computer Science
• Categoria: Programming in JavaScript

All of JavaScript's newest features, in depth, made easy to understand.

JavaScript is a rapidly changing language and it can be challenging to keep up with all the new toys being added. JavaScript: The New Toys explores the newest features of the world's most popular programming language while also showing readers how to track what's coming next. After setting the stage by covering who manages the process of improving JavaScript, how new features get introduced, terminology, and a high-level overview of new features, it details each new or updated item in depth, with example uses, possible pitfalls, and expert recommendations for updating old habits in light of new features. JavaScript: The New Toys:

• Covers all the additions to JavaScript in ES2015-ES2020 plus a preview of what's coming next
• Explores the latest syntax: nullish coalescing, optional chaining, let and const, class syntax, private methods, private fields, new.target, numeric separators, BigInt, destructuring, default parameters, arrow functions, async functions, await, generator functions, ... (rest and spread), template literals, binary and octal literals, ** (exponentiation), computed property/method names, for-of, for-await-of, shorthand properties, and others
• Details the new features and patterns including modules, promises, iteration, generators, Symbol, Proxy, reflection, typed arrays, Atomics, shared memory, WeakMap, WeakSet, and more
• Highlights common pitfalls and explains how to avoid them
• Shows how to follow the improvements process and even participate in the process yourself
• Explains how to use new features even before they're widely supported

With its comprehensive coverage and friendly, accessible style, JavaScript: The New Toys provides an invaluable resource for programmers everywhere, whether they work in web development, Node.js, Electron, Windows Universal Apps, or another JavaScript environment.

1
The New Toys in ES2015–ES2020, and Beyond

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WHAT'S IN THIS CHAPTER?

• Definitions, who's who, and terminology
• Explanation of JavaScript versions (ES6? ES2020?)
• What are the “new toys”?
• The process driving new JavaScript features
• Tools for using next-generation JavaScript

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CODE DOWNLOADS FOR THIS CHAPTER

You can download the code for this chapter at https://thenewtoys.dev/bookcode or https://www.wiley.com/go/javascript-newtoys.

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JavaScript has changed a lot in the last few years.

If you were an active JavaScript developer in the 2000s, for a while there you could be forgiven for thinking JavaScript was standing still. After the 3rd Edition specification in December 1999, developers were waiting fully 10 years for the next edition of the specification. From the outside, it seemed like nothing was happening. In fact, lots of work was being done; it just wasn't finding its way into the official specification and multiple JavaScript engines. We could (but won't) spend an entire chapter—if not a book—on what various different groups in important positions vis-à-vis JavaScript were doing and how they couldn't agree on a common path forward for some time. The key thing is that they ultimately did agree on a way forward, at a fateful meeting in Oslo in July 2008 after much advance negotiation. That common ground, which Brendan Eich (creator of JavaScript) later called Harmony, paved the way for the 5th Edition specification in December 2009 (the 4th Edition was never completed), and laid the basis for ongoing progress.

And my, how things have progressed.

In this chapter, you'll get an overview of the new features since 2009 (which the rest of the book covers in detail). You'll learn who's in charge of moving JavaScript forward, what process is now used to do so, and how you can keep track of what's coming and get involved if you like. You'll learn about tools you can use to write modern JavaScript today, even if you have to target environments that haven't kept up.

DEFINITIONS, WHO'S WHO, AND TERMINOLOGY

To talk about what's going on with JavaScript, we need to define some names and common terminology.

Ecma? ECMAScript? TC39?

What we think of as “JavaScript” is standardized as “ECMAScript” by Ecma International,¹ a standards organization responsible for multiple computing standards. The ECMAScript standard is ECMA-262. The people in charge of the standard are members of Ecma International Technical Committee 39 (“TC39”), charged with “Standardization of the general purpose, cross platform, vendor-neutral programming language ECMAScript. This includes the language syntax, semantics, and libraries and complementary technologies that support the language.”² They manage other standards as well, such as the JSON Syntax Specification (ECMA-404), and notably the ECMAScript Internationalization API Specification (ECMA-402).

In this book and in common usage, JavaScript is ECMAScript and vice versa. Sometimes, particularly during the decade of different groups doing different things, “JavaScript” was used to specifically mean the language Mozilla was developing (which had several features that either never made it into ECMAScript, or changed markedly before they did), but since Harmony that usage is increasingly outdated.

ES6? ES7? ES2015? ES2020?

Having all these various abbreviations can be confusing, not least because some have edition numbers but others have years. This section explains what they are and why there are two kinds of them.

Up through the 5th Edition, TC39 referred to versions of the specification via their edition number. The full title of the 5th Edition spec is:

• Standard ECMA-262
• 5th Edition / December 2009
• ECMAScript Language Specification

Since “ECMAScript 5th Edition” is a bit of a mouthful, saying “ES5” was the natural thing to do.

Starting with the 6th Edition in 2015, TC39 adopted a continual improvement process where the specification is a living editor's draft³ with annual snapshots. (More about that later in this chapter.) When they did that, they added the year to the language name:

• Standard ECMA-262
• 6th Edition / June 2015
• ECMAScript® 2015 Language Specification

So the ECMAScript 6th Edition standard (“ES6”) defines ECMAScript 2015, or “ES2015” for short. Prior to publication, “ES6” became a buzzword of its own and is still in common usage. (Unfortunately, it's often used inaccurately, referring not just to features from ES2015, but also to features that came afterward in ES2016, ES2017, and so on.)

That's why there are two styles, the style using the edition (ES6, ES7, …) and the style using the year (ES2015, ES2016, …). Which you use is up to you. ES6 is ES2015 (or sometimes, incorrectly, ES2015+), ES7 is ES2016, ES8 is ES2017, and so on through (as of this book's release) ES11, which is ES2020. You'll also se...