The 'thisArg' parameter should be used to type 'this' in callbacks to map, filter, etc.

[e-cloud]

TypeScript Version: (2.2.0-dev.20161128)

Code

tets.ts

class A {
    options: any[]
    addOptions(options: any[]) {
        if (!this.options) {
            this.options = [];
        }
        options.forEach(function (item) {
            this.options.push(item);
        }, this);
        return this;
    }
}

tsc --module commonjs --noImplicitThis --noEmit test.ts

Expected behavior:
compile with no error output

Actual behavior:
test.ts(8,13): error TS2683: 'this' implicitly has type 'any' because it does not have a type annotation.

As some built-in method of array can assign this, could it be inferred through the scopes?

[DanielRosenwasser]

forEach should actually contextually type this based on the thisArg, and that will work.

But thisArg isn't used for the callback types in lib.d.ts's declarations for forEach, map, filter, etc. right now.

[mhegazy]

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.

[e-cloud]

@mhegazy I've fixed the source. But how can i write the tests for changes? The test suite is so huge, it could take time to figure out. So ask you for how is more direct.

[jcalz]

Should this be reopened in light of #16223?