30 seconds of codeBack to Home
Inverts the key-value pairs of an object, without mutating it. The corresponding inverted value of each inverted key is an array of keys responsible for generating the inverted value. If a function is supplied, it is applied to each inverted key.
Array.prototype.reduce() to invert the key-value pairs of an object and apply the function provided (if any).
Omit the second argument,
fn, to get the inverted keys without applying a function to them.