Get all subsets of an array

JavaScript version

const getSubsets = (arr) => arr.reduce((prev, curr) => prev.concat(prev.map((k) => k.concat(curr))), [[]]);

TypeScript version

const getSubsets = <T,>(arr: T[]): T[][] => (
    arr.reduce((prev, curr) => prev.concat(prev.map((k) => k.concat(curr))), [[]] as T[][])
);

Examples

getSubsets([1, 2]); // [[], [1], [2], [1, 2]]
getSubsets([1, 2, 3]); // [[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3]]