Typescript: Regression for Headers global on nightly

[pocesar]

TypeScript Version: 2.6.0-dev.20170826

Code

    const headers = new Headers({
      Accept: 'application/json',
      'Content-Type': 'application/json'
    })

Expected behavior:

Works

Actual behavior:

Argument of type '{ Accept: string; 'Content-Type': string; }' is not assignable to parameter of type 'Headers | string[][]'.
  Object literal may only specify known properties, and 'Accept' does not exist in type 'Headers | string[][]'.

According to the docs https://developer.mozilla.org/en-US/docs/Web/API/Headers/Headers it's an object, not a string[][]

[mhegazy]

Acctually based on https://fetch.spec.whatwg.org/#headers-class, it can be Headers | string[][]| object

[mhegazy]

@vrachels this is a different issue. please file a new ticket to track that.

[NeoLegends]

I'd just like to add some feedback to this: these kinds of regressions are _extremely_ annoying. Seems like every update of TypeScript (even the minor ones) break my build and I have to adapt my code / revert to a previous version just because of small stuff like this. Please increase the test coverage for the typings!