Back in 2012, the WHATWG set out to document the differences between the ECMAScript 5.1 specification and the compatibility and interoperability requirements for ECMAScript implementations in web browsers.
- figuring out implementation differences for various non-standard features;
- filing browser bugs to get implementations to converge;
- and finally writing specification text for the common or most sensible behavior, hoping it would one day be upstreamed to ECMAScript.
That day has come.
The infamous “string HTML methods”:
String.prototype.substr(start, length), and
ECMAScript Annex B, which specifies things like
-->). As of ECMAScript 2015, Annex B fully defines this syntax.
__lookupSetter__ methods on
Object.prototype are defined in ECMAScript Annex B, as is
Until recently, the HTML Standard lacked a precise definition of the
Location objects. As you might imagine, these are fairly important objects, so having them be underdefined was not great for the web. (Note that the global object used for documents is the
WindowProxy object, which serves as a proxy and security boundary for the
Each navigable frame (top-level tab,
<iframe> element, et cetera) is called a browsing context in the HTML Standard. A browsing context has an associated
Window object. As you navigate a browsing context, the associated
Window object changes. But the whole time, the
WindowProxy object stays the same. Ergo, one
WindowProxy object is a proxy for many
To make matters more interesting, scripts in these different browsing contexts can access each other, through
window.open(), et cetera. The same-origin policy generally forbids code from one origin from accessing code from a different origin, which prevents evil.com from prying into bank.com. The two legacy exceptions to this rule are the
Location objects, which have some properties that can be accessed across origins.
document.domain makes this even trickier, as it effectively allows you to observe a
Location object as cross-origin initially, and same-origin later, or vice versa. Since the object remains the same during that time, the same-origin versus cross-origin logic needs to be part of the same object and cannot be spread across different classes.
Defining this all in detail has been a multi-year effort spearheaded by Bobby Holley, Boris Zbarsky, Ian Hickson, Adam Barth, Domenic Denicola, and Anne van Kesteren, and completed in the “define security around
Location objects properly” pull request. The basic setup we ended up with is that
Location objects have specific cross-origin branches in their internal method implementation. These take care to only expose specific properties, and even for those properties, generating specific accessor functions per origin. This ensures that cross-origin access is not inadvertently allowed through something like
Object.getOwnPropertyDescriptor(otherWindowProxy, "window").get. After filtering, a
WindowProxy object will forward to its
Window object as appropriate, whereas a
Location object simply gives access to its own properties.
Having these objects defined in detail will make it easier for implementations to refactor, and for new novel implementations like Servo to achieve web-compatibility. It will reduce debugging time for web developers after implementations have converged on the edge cases. And it drastically simplifies extending these objects, as well as placing new restrictions upon them, within this well-defined subsystem. Well-understood, stable foundations are the key to future extensions.
(Many thanks to Bobby Holley for his contributions to this post.)
One thing we’ve been meaning to do more of is tell our blog readers more about new features we’ve been working on across WHATWG standards. We have quite a backlog of exciting things that have happened, and I’ve been nominated to start off by telling you the story of
charset attributes applied. The end result can be seen in a number of places in the HTML Standard, most notably in the definition of the
script element and the scripting processing model sections. At the request of the Edge team, we also added support for worker modules, which you can see in the section on creating workers. (This soon made it over to the service workers spec as well!) To wrap things up, we included some examples: a couple for
<script type="module">, and one for module workers.
Of course, specifying a feature is not the end; it also needs to be implemented! Right now there is active implementation work happening in all four major rendering engines, which (for the open source engines) you can follow in these bugs:
And there's more work to do on the spec side, too! There's ongoing discussion of how to add more advanced dynamic module-loading APIs, from something simple like a promise-returning
self.importModule, all the way up to the experimental ideas being prototyped in the whatwg/loader repository.
(This post is a rough copy of an email I sent to the mailing list.)
I wanted to remind the community that currently all WHATWG standards are being developed on GitHub. This enables everyone to directly change standards through pull requests and start topic-based discussion through issues.
GitHub is especially useful now that the WHATWG covers many more topics than “just” HTML, and using it has already enabled many folks to contribute who likely would not have otherwise. To facilitate participation by everyone, some of us have started identifying relative-easy-to-do issues across our GitHub repositories with the label “good first bug”. (See also good first bugs on Bugzilla. New issues go to GitHub, but some old ones are still on Bugzilla.) And we will also continue to help out with any questions on #whatwg IRC.
You should be able to find the relevant GitHub repository easily from the top of each standard the WHATWG publishes. Once you have a GitHub account, you can follow the development of a single standard using the “Watch” feature.
There are no plans to decommission the mailing list — but as you might have noticed, new technical discussion there has become increasingly rare. The mailing list is still a good place to discuss new standards, overarching design decisions, and more generally as a place to announce (new) things.
When there’s a concrete proposal or issue at hand, GitHub is often a better forum. IRC also continues to be used for a lot of day-to-day communications, support, and quick questions.
It’s been several months now since maintenance of the HTML Standard moved from a mostly-private Subversion repository to the whatwg/html GitHub repository. This move has been even more successful than we hoped:
- We now have thirty-seven contributors who have landed one or more patches, and have merged over 250 pull requests in total. That’s almost two new contributors each week since the move!
- We’ve worked to curate a list of good first bugs to introduce newcomers to the community and the standard, and worked hard to improve the onboarding experience for building the standard.
- With help from the community, the standard's gender pronoun disparity has been significantly improved. (See The happy case of pronouns and HTML.)
- Sponsored by Mozilla, we have applied to Outreachy and Richa Rupela is now helping us write the HTML Standard.
- We have collaborated with TC39—who thankfully moved to GitHub around the same time—to remove some longstanding discrepancies between HTML and ECMAScript.
- We've made many, many small fixes to better match the reality of what is implemented in browsers, mostly in response to feedback from browser developers.
Aside from defining the HTML language, the HTML Standard defines the processing model around script execution, the fundamentals of the web’s security model, the web worker API for parallel script execution, and many more aspects that are core to the web platform. If you are interested in helping out, please reach out on IRC or GitHub.