Typescript: Can't construct new Map() with return from mapping function

Question

I have this code (only relevant parts here):

interface Page {
  name: String;
  displayName: String;
}


let pages: Page[] = [{name: 'x', displayName: 'y'}, {name: 'a', displayName: 'b'}];
let m = new Map(pages.map(page => [page.name, page.displayName]));

And I get this error for it (from tslint):

Argument of type 'String[][]' is not assignable to parameter of type 'Iterable<[{},{}]>'

These types are defined as such:

map<U>(callbackfn: (value: T, index: number, array: T[]) => U, thisArg?: any): U[];

interface MapConstructor {
    new <K, V>(): Map<K, V>;
    new <K, V>(iterable: Iterable<[K, V]>): Map<K, V>;
    prototype: Map<any, any>;
}

(both types are from here)

What am I doing wrong?
Thanks!

Answer 1

What am I doing wrong?

Nothing. The TypeScript type inference system is struggling a bit, help it along with a type annotation to tell it that you mean a tuple[string,string] not a multi dimensional array string[][]:

var pages:{
  name: string;
  displayName: string;
}[];

var pagesForMap = pages.map((page):[string,string] => [page.name, page.displayName]);
var pagesNames = new Map(pagesForMap);

Tuple types are covered here : http://basarat.gitbooks.io/typescript/content/docs/types/type-system.html