Saturday, June 23, 2007

Crockford's revisions to ECMAScript

The ECMAScript standard is undergoing growing pains right now, and for the first time since 1999, it looks like major revisions to the language may take effect soon. Douglas Crockford has recommendations of his own. While I don't have any strong feelings about the new features he requests (they can mostly be implemented in the JavaScript we already have), his Corrections are mostly sane things that will remove a lot of the suckiness from the current standard:

  1. Reserved words
  2. Standardize implementation of trailing commas in object literals and arrays
  3. Make arguments object a true array
  4. Tail recursion optimization
  5. Deprecate primitive type wrappers, the with statement, semicolon insertion, arguments.callee, typeof, and eval.

It looks like Brendan Eich is well aware of Crockford's longstanding laments, particularly against the with statement and the reserved words restrictions, and has addressed them in the draft spec for ECMA-262 v4.

Crockford objects to restricting the use of reserved keywords in object definitions as unnecessary. According to his argument, usage such as:

var o = {
    class: 'style', 
    with: function (n) { return n+'a top hat'; }

will preserve the original use of these names, as the names are merely being used for scoped member properties; they cannot be confused in this context, syntactically, with the "official" uses of these keywords. (This is, apparently, why the JSON spec requires double-quoted property names.) However, it seems this restriction is in place mainly to make possible the use of the with keyword; consider:

with (o) {
   class = 'none';

If using these keywords were legal above, their use with the with statement here invites syntax hell.

I for one would be happy to see the demise of the with keyword. It breaks with JavaScript's function-level scoping, and creates more problems than it's meant to solve. It "feels" uncharacteristic of the language, since it promotes an object's properties from "property" status into "variable" status, blending them indiscriminately into the surrounding scope. JavaScript has enough trouble affording decent namespacing as it is; this "feature" smacks of bad practice.

More than adding new features, we could use a "trimming-down" phase to the language. While Mozilla toils at turning JavaScript into Python and other power-players at ECMA (presumably MS?) seek to remake the spec in the image of Java or C#, I'm mostly happy with the way it is - just please, for God's sake, fix the problems that are currently there before bounding into a new round of ill-conceived feature bloat.

We front-end developers are lucky to be enjoying a golden age of JavaScript. But the clouds of confusion and incompatibility are on the horizon. I don't see a compelling reason to add Java-style classical inheritance to the language, and I see even less a possibility of the vendors agreeing to ship timely implementations of this new spec.

Surely wiser heads than mine are laboring on this problem. But I guess I'm just not seeing that JavaScript falls short in ways that warrant changing it beyond recognition.

No comments: