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Custom elements ES6/ES5 syntax compromise, was: document.register and ES6

From: Dimitri Glazkov <dglazkov@google.com>
Date: Thu, 14 Feb 2013 13:48:06 -0800
Message-ID: <CADh5Ky0++iSBcd1+rXujm93LVcV7obPPKzkTAsoYS3+OnHfrzA@mail.gmail.com>
To: public-webapps <public-webapps@w3.org>
Cc: Scott Miles <sjmiles@google.com>, Daniel Buchner <daniel@mozilla.com>, Erik Arvidsson <arv@chromium.org>, Boris Zbarsky <bzbarsky@mit.edu>, Anne van Kesteren <annevk@annevk.nl>

I propose just a bit of sugaring as a compromise, but I want to make
sure this is really sugar and not acid, so please chime in.

1) We give up on unified syntax for ES5 and ES6, and instead focus on
unified plumbing
2) document.register returns a custom element constructor as a result,
just like currently specified:
3) There are two ways to register an element: with a constructor and
with a prototype object.
4) When registering with the constructor (aka the ES6 way), you must
supply the constructor/class as the "constructor" member in the
ElementRegistrationOptions dictionary
5) If the constructor is supplied, element registration overrides
[[Construct]] internal function as described in
6) Registering with a prototype object (aka the current way) uses the
"prototype" member in ElementRegistrationOptions dictionary and works
roughly as currently specified
7) If the prototype object is supplied, the constructor is generated
as two steps:
  a) Instantiate the platform object
  b) Call "created" callback from lifecycle callback interface bound to "this"
8) We remove any sort of shadow tree creation and the corresponding
template argument from the spec. Shadow tree management is left
completely up to the author.

Effectively, the "created" callback becomes the poor man's
constructor. It's very easy to convert from old syntax to new syntax:

The prototype way:

function MyButton() {
  // do constructor stuff ...
MyButton.prototype = Object.create(HTMLButtonElement.prototype, {
MyButton = document.register(‘x-button’, {
  prototype: MyButton.prototype,
  lifecycle: {
     created: MyButton

The constructor way:

function MyButton() {
 // do constructor stuff ...
MyButton.prototype = Object.create(HTMLButtonElement.prototype, {
document.register(‘x-button’, {
 constructor: MyButton,

This is nearly the same approach as what  Scott sketched out here:
http://jsfiddle.net/aNHZH/7/, so we already know it's shimmable :)

What do you think?

Received on Thursday, 14 February 2013 21:48:41 UTC

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