To find elements in array that are not in another array with JavaScript, we use the filter and includes method.

For instance, we write

const a1 = ["a", "b", "c", "t"];
const a2 = ["d", "a", "t", "e", "g"];

console.log(a2.filter((x) => !a1.includes(x)));

to call filter with a callback that checks if item x in a2 isn’t a1 with includes and negation.

An array with the items in a2 not in a1 is returned.