Type 'any[]' is not assignable to type '[any, any]' when constructing a Map from array of entries

[mohsen1]

During my work at webpack/webpack#6862 I noticed this error.

TypeScript Version: 2.7.8-rc

Search Terms:

Code
https://github.com./webpack/webpack/blob/master/lib/util/objectToMap.js

function objectToMap(obj) {
	return new Map(Object.keys(obj).map(key => [key, obj[key]]));
};

Expected behavior:
No error

Actual behavior:

lib/util/objectToMap.js:9:17 - error TS2345: Argument of type 'any[][]' is not assignable to parameter of type 'Iterable<[any, any]>'.
  Types of property '[Symbol.iterator]' are incompatible.
    Type '() => IterableIterator<any[]>' is not assignable to type '() => Iterator<[any, any]>'.
      Type 'IterableIterator<any[]>' is not assignable to type 'Iterator<[any, any]>'.
        Types of property 'next' are incompatible.
          Type '{ (value?: any): IteratorResult<any[]>; (value?: any): IteratorResult<any[]>; }' is not assignable to type '{ (value?: any): IteratorResult<[any, any]>; (value?: any): IteratorResult<[any, any]>; }'.
            Type 'IteratorResult<any[]>' is not assignable to type 'IteratorResult<[any, any]>'.
              Type 'any[]' is not assignable to type '[any, any]'.
                Property '0' is missing in type 'any[]'.

9  return new Map(Object.keys(obj).map(key => [key, obj[key]]));
                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[DanielRosenwasser]

I think this looks like a duplicate of #11152.

[MartinJohns]

The tuple is inferred to be an array. As a temporary workaround you can just specify the exact type when calling map:

array.map<[Type1, Type2]>(key => [key, obj[key]])

That will make it explicit that you want a tuple.

[mhegazy]

in a .js file you can cast using /** @type ... */:

function objectToMap(obj) {
	return new Map(Object.keys(obj).map(key => /** @type [string, string] */ ([key, obj[key]]));
};  

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.