Typescript: React emit should have an '_extends' helper for spread attributes

[DanielRosenwasser]

This is effectively a polyfill for Object.assign, and we should consider emitting the specific helper.

[mhegazy]

can you elaborate on the request, and why?

[RyanCavanaugh]

We currently emit a call to React.__spread which has been deprecated for a while now (and might be gone soon?). The official JSX transformer calls _extends which is initialized with Object.assign || (object.assign polyfill)

[kuon]

__spread is gone in react 15.0. which means typescript 1.8.9 cannot compile TSX with react 15.0.

My workaround:

import {assign} from 'lodash';
(React as any).__spread = assign;

Workaround without lodash: https://github.com/Microsoft/TypeScript/issues/7270#issuecomment-207138701

[gaearon]

@kuon Thank you for the workaround.
I would suggest using object-assign npm module directly. It is what React uses in 15.

[kuon]

Yeah, but as I had lodash in my project, with typescript definition and all, it was easier.

[gaearon]

We’ll temporarily bring it back to avoid breaking everyone using TS: https://github.com/facebook/react/pull/6444. However the method is deprecated and will go away in the next major release.

[DanielRosenwasser]

Thanks so much @gaearon, we really appreciate the temporary rollback.

[kuon]

Proper workaround without lodash:

In a *.d.ts file, add:

declare module 'object-assign' {
    function Assign(target: any, source: any): any;
    module Assign { }
    export = Assign;
}

In your main *.ts file, reference your lib file and add:

import * as assign from 'object-assign';
(React as any).__spread = assign;

For clarity, you might want to add object-assign as an explicit dependency in your package.json until this is fixed.

[DanielRosenwasser]

A fix is out in #7952. Ideally we can get the change into the next nightly.

[jgillich]

Just in case someone else wonders, ES6 Object.assign works as well:

(React as any).__spread = Object.assign;

(but you need core-js or another polyfill if you're not targeting ES6).

[DanielRosenwasser]

A fix should be out in our nightlies tonight. We'll potentially port the fix to our 1.8 branch.

[DanielRosenwasser]

This should be fixed in TypeScript 1.8.10, which is now on npm and NuGet.

[basarat]

Now that we have this for react, how about getting this for normal TypeScript (primarily because libraries out there e.g. redux love it) {...foo,{withSomethingMore}}

: https://github.com/Microsoft/TypeScript/issues/2103 :rose: