var indexOf = require('array-index-of');
var index = indexOf([1, 2, 3], 2);  // 1
var index2 = indexOf([{a: 1}, {a: 2}], {a: 2}, function(inArr, target) {
  return inArr.a === target.a;
});  // 1

// or you can override #indexOf of an Array object
var override = require('array-index-of').override;
var arr = override([1, 2]);
var index = arr.indexOf(2, function(a, b) { return (a + 1) === b; });
console.log(index); // 0