30-seconds-of-code/snippets/array-difference.md

Array difference

Create a Set from b, then use Array.filter() on a to only keep values not contained in b.

const difference = (a, b) => { const s = new Set(b); a.filter(x => !s.has(x)); };
// difference([1,2,3], [1,2,4]) -> [3]

This function can also be used to generate the symmetric difference or disjunctive union by swapping the arrays and combining the results.

const symmetricDifference = (a, b) => [...difference(a,b), ...difference(b,a)];
// difference([1,2,3], [1,2,4]) -> [3,4]