A core of JavaScript (the so-called “good parts”) is elegant, but that core is often obscured by quirks. This introduction is the first of a series of blog posts that looks at twelve common quirks and how to best deal with them:

[This post is part of a series on JavaScript quirks.]

JavaScript is very tolerant when it comes to accepting values. For example, everywhere it expects a number, it does not reject values from other types, but tries to convert them:

    > '5' - '2'
    3
    > '5' * '2'
    10

Automatic conversion to boolean is rarely problematic and often useful. It is covered here as a preparation for later – we’ll use it to work around quirks. Automatic conversion to string, however, can cause problems.

With Blink, Google has created a permanent fork of the WebKit HTML engine. This blog post mentions a few interesting facts that provide context for that decision.

JavaScript usually automatically converts values to the type that a method or operator needs, which can lead to a variety of bugs. As a counter-measure, Brian McKenna (@puffnfresh) suggests using the following code for your tests:

    Object.prototype.valueOf = function () {
        throw new Error('Use an explicit toString');
    };

Quick tip (via David Klassen): The following shell command lists all (highly experimental!) ECMAScript Harmony [1] features that can be switched on in Node.js.

    node --v8-options | grep harmony

Most people know that ECMAScript is the language standard behind JavaScript [1]. Fewer people know that its name comes from Ecma International, the organization managing this standard. Interestingly, that organization started as “European Computer Manufacturers Association (ECMA)”, but renamed itself to “Ecma International” in 1994. That was done to reflect its increasingly international focus. Ecma is now not considered an acronym, any more. Ecma International is located in Geneva. In contrast, TC39 [1], the Ecma-hosted committee evolving ECMAScript, is rather USA-centric (true to where JavaScript was created and who created it) and usually meets somewhere in California.

2013-12-23: A new blog post on ParallelJS (as Parallel JS is now called) supersedes this post.

Parallel JS will soon be included in Firefox Nightly builds. This project was initially called River Trail [1]. It automatically parallelizes code that uses the ParallelArray type and its array-like methods (map() etc.). [Source of this post: “Parallel JS lands” by Nicholas D. Matsakis.]

TC39 [1] is the committe that currently plans ECMAScript 6 (code-named ECMAScript.next), the next version of the JavaScript language standard. January 29–31, they had another meeting. Thanks to Rick Waldron’s notes, we can read up on what has been decided. This blog post describes the highlights. Previous blog posts summarized prior meetings.

(Note: a blog post on the March TC39 meeting will be posted at some time in the future.)

[Update 2015-02-15] Newer version of this blog post: “Classes in ECMAScript 6 (final semantics)”

In JavaScript, it is difficult to create sub-constructors of built-in constructors such as Array. This blog post explains the problem and possible solutions – including one that will probably be chosen by ECMAScript 6. The post is based on Allen Wirfs-Brock’s slides from a presentation he held on January 29, during a TC39 meeting.

This blog post explores the Lehmer code, a way of mapping integers to permutations. It can be used to compute a random permutation (by computing a random integer and mapping it to a permutation) and more.