createMap.js

Array.prototype.createMap = Array.prototype.createMap || function(callback) {
	var newArray = [];
  for (var i = 0; i < this.length; i++) {
  	var result = callback(this[i], i);
    newArray.push(result);
  }
  return newArray;
}

var start = [1, 2, 3];

var transformedArray = start.createMap(function(value, index) {
	return value + 1;
});

console.log(transformedArray);