# Array symmetric difference based on function

JavaScript, Array · Oct 18, 2020

Returns the symmetric difference between two arrays, using a provided function as a comparator.

- Use
`Array.prototype.filter()`

and`Array.prototype.findIndex()`

to find the appropriate values.

const symmetricDifferenceWith = (arr, val, comp) => [ ...arr.filter(a => val.findIndex(b => comp(a, b)) === -1), ...val.filter(a => arr.findIndex(b => comp(a, b)) === -1) ]; symmetricDifferenceWith( [1, 1.2, 1.5, 3, 0], [1.9, 3, 0, 3.9], (a, b) => Math.round(a) === Math.round(b) ); // [1, 1.2, 3.9]