The difference between map function and each function in jquery _ function

The use of each function in jquery looks almost the same as the map function, but there is a difference.

One important difference is that each returns the original array, and no new array is created. The map method returns a new array. If you use a map if it is not necessary, you can create a waste of memory.

e.g.

  var items = [1,2,3,4];  $.each (items, function () {
      alert (' it ' + this);
  });
  var newitems = $.map (items, function (i) {return
      i + 1;
  });
  NewItems is [2,3,4,5]

When you use each, you change the original items array, and when you use map, do not change items, just create a new array.

e.g.

    var items = [0,1,2,3,4,5,6,7,8,9];    var itemslessthanequalfive = $.map (items, function (i) {
      //Removes all items > 5
      if (i > 5) 
        ret Urn null;
      return i;
    });
      Itemslessthanequalfive = [0,1,2,3,4,5]

This is also true when an array is required for deletion, so the error of using each or map for deletion is quite serious.