Array.prototype.map()

The map() function is the ringleader of the bunch. It simply applies the callback function on each item in the array.

Note

Syntax: arr.map(callback [, thisArg]);

Parameters:

callback(): This function produces an element for the new array, receiving these arguments:
- currentValue: This argument gives the current element being processed in the array
- index: This argument gives the index of the current element in the array
- array: This argument gives the array being processed
thisArg(): This function is optional. The value is used as this when executing callback.

Examples:

var   integers = [1,-0,9,-8,3],   numbers = [1,2,3,4],   str = 'hello world how ya doing?'; // map integers to their absolute values console.log(integers.map(Math.abs));  // multiply an array of numbers by their position in the array console.log(numbers.map(function(x, i){return x*i}) );  // Capitalize every other word in a string. console.log(str.split(' ').map(function(s, i){   if (i%2 == 0) {     return s.toUpperCase();   }   else {     return s;   } }) );

Note

While the Array.prototype.map method is a standard method for the Array object in JavaScript, it can be easily extended to your custom objects as well.

MyObject.prototype.map = function(f) {   return new MyObject(f(this.value)); };