Invert keys and values of an object

JavaScript version
const invert = (obj) => Object.keys(obj).reduce((res, k) => Object.assign(res, { [obj[k]]: k }), {});
// Or
const invert = (obj) => Object.fromEntries(Object.entries(obj).map(([k, v]) => [v, k]));
Examples
invert({ a: '1', b: '2', c: '3' }); // { 1: 'a', 2: 'b', 3: 'c' }