All keys are strings in JavaScript – just use map
:
const sizes: number[] = Object.keys(foo).map(Number);
This’ll only work for numeric strings – if it’s a European string involving decimals, for instance, it’ll be NaN
, and that never ends well.
console.log(Number("10,7"));
Or change either of your types:
const sizes: string[] = Object.keys(foo);
Or:
type Foo = { [key: string]: string };