Compare true/false array with other array

Question

What is the quickest way to compare two arrays and return a third array containing the values from array2 where the associated values from array1 are true?

const array1 = [true, false, false, true];
const array2 = ['a', 'b', 'c', 'd'];

The result should be:

const result = ['a', 'd'];

Answer 1

Use filter.

const array1 = [true, false, false, true];
const array2 = ['a', 'b', 'c', 'd'];
const res = array2.filter((_, i) => array1[i]);
console.log(res);

ES5 syntax:

var array1 = [true, false, false, true];
var array2 = ['a', 'b', 'c', 'd'];
var res = array2.filter(function(_, i) {
  return array1[i];
});
console.log(res);