DragEvent should accept a DragEventInit inheriting from MouseEventInit

[WojciechP]

TypeScript Version: master, eef7d8b

Code

let ev = new DragEvent('drag', {clientX: 40})

Expected behavior:
This should typecheck, because the second argument to new DragEvent should inherit from MouseEventInit: https://developer.mozilla.org/en-US/docs/Web/API/DragEvent/DragEvent

Actual behavior:
Typechecking fails, because the typings only allow dataTransfer property.

[kitsonk]

These typings are imported from files generated by Microsoft/TSJS-lib-generator. The contribution guidelines to that are documented here.

[mhegazy]

As @kitsonk pointed out. PRs welcomed. You can find more information about contributing lib.d.ts fixes at https://github.com/Microsoft/TypeScript/blob/master/CONTRIBUTING.md#contributing-libdts-fixes.

[jakebailey]

Just looking at old issues; this was fixed back in #25944.