What does the type { [key: string]: boolean; } mean?

Question

Run into such thing lately, a function declaration:

static required(control: AbstractControl): {
        [key: string]: boolean;
    };

Wh

Answer 1

This is a key/value structure. The key is a string and the value is a boolean. For example:

let map : { [key: string]: boolean} = {};
map["foo"] = true;
map["bar"] = false;
map.foo = true;
map["foobar"] = "foo"; // Throws exception
map[1] = true; // Curiously doesn't throws exception

Check this sample on the Typescript Playground.

Indexable Types.