Outdated WHATWG DOM Event interface and init

[KamiQuasi]

TypeScript Version: 2.4.0 / nightly (2.5.0-dev.201xxxxx)

Code

// A *self-contained* demonstration of the problem follows...
// Test this by running `tsc` on the command-line, rather than through another build tool such as Gulp, Webpack, etc.
document.dispatchEvent(new CustomEvent('test-event', { detail: { foo: 'bar' }, bubbles: true, composed: true }));

Expected behavior:
Utilizing the 'composed' property should work. As per the WHATWG Living Standard the 'scoped' and 'deepPath' properties of an Event have been replaced with 'composed' and 'composedPath' respectively (see https://dom.spec.whatwg.org/)

Actual behavior:
Argument of type '{ detail: { term: string; }; bubbles: true; composed: boolean; }' is not assignable to parameter of type 'CustomEventInit'.
Object literal may only specify known properties, and 'composed' does not exist in type 'CustomEventInit'.

[kitsonk]

composed is part of the ShadowDom v1 specification and it seems like it is only implemented in Chrome and Firefox at the moment.

That being said, changes to these interfaces are contributed via the TSJS-lib-generator and contribution guidelines can be found here

Also, interfaces are open ended, so you could easily add this to your local project, knowing that you were going to run in an environment where this was supported:

declare global {
  interface Event {
    readonly composed: boolean;
  }
}

[KamiQuasi]

@kitsonk hoping I didn't misread the contribution guidelines on the TSJS-lib-generator repo, but it seemed to say to make changes there I should submit an issue here to reference. I've submitted a PR on that repo that should adjust this (microsoft/TypeScript-DOM-lib-generator#284). The main reason I wanted to get this change in was for compatibility with the webcomponents v1 polyfill, which also implements the composed and composedPath properties.

[kitsonk]

Apologies, missed the linked issue... 😊