JS foreach and map usage

ForEach:

foreach is the most basic one of the new array methods in ECMA5, that is, traversal, loop. For example, the following example:
[1, 2, 3, 4].foreach (alert);
Equivalent to the following for loop:

var array = [1, 2, 3, 4];
for (var i = 0, length = Array.Length i < length; i++) {
 alert (array[i]);

The function callback in the Foreach method supports 3 parameters, the 1th is the array content that is traversed, the 2nd is the corresponding array index, and the 3rd is the array itself.

[].foreach (function (value, index, array) {
  //...
});

For example:

var array = [1,2,3];
Array.foreach (function (Val,index,arr) {
    console.log (' val: ' +val); => 1,2,3 console.log
    ("index:" + index); =>0,1,2
    Console.log (arr); => [1,2,3]
})
output in the console is:

Because foreach is essentially a loop, it outputs three of times an array.


Map:

The map method of an array refers to the mapping, in which the original array is "mapped" to the corresponding new array.

Array.map (callback,[thisobject]);

Use of Map:
Map receives three parameters like foreach, and he can map the original array to the new array.

var data=[1,3,4]

var squares=data.map (function (Val,index,arr) {
  console.log (arr[index]==val);  ==> true return
  val*val           
})
Console.log (squares);        ==> [1, 9, 16]

Note: These two methods are not supported by browsers below IE9, and can be expanded from the array prototype to achieve all of these functions:

if (typeof Array.prototype.forEach!= "function") {
  Array.prototype.forEach = function () {/
    * Custom Function Implementation * * * *
  };< c10/>}