Example introduction to the difference between map function and each function in jquery_jquery

​The usage of each function and map function in jquery seems to be similar, but in fact there is a little difference.

​One of the important differences is that each returns the original array and does not create a new array. The map method will return a new array. If map is used unnecessarily, memory may be wasted.

For example:

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

When using each, the original items array is changed, but when using map, the items are not changed, but a new array is created.

For example:

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) 
return null; 
return i; 
}); 
// itemsLessThanEqualFive = [0,1,2,3,4,5]

The same is true when an array needs to be deleted, so the consequences of incorrectly using each or map when deleting are quite serious.