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TS JS Deno

Returns every element that exists in any of the two arrays once, after applying the provided function to each array element of both.

Create a Set by applying all fn to all values of a. Create a Set from a and all elements in b whose value, after applying fn does not match a value in the previously created set. Return the last set converted to an array.

const unionBy = (a: any[], b: any[], fn: MapFunc) => {
const s = new Set(;
return Array.from(new Set([...a, ...b.filter((x) => !s.has(fn(x)))]));
unionBy([2.1], [1.2, 2.3], Math.floor); // [2.1, 1.2]