Array map()

map() accepts two arguments:

a function to run on each item and
an optional scope object

map() runs the given function on every item and returns the result of each function call in an array.

The function passed in receives three arguments:

the array item value,
the position of the item in the array
the array object itself.

 
<!DOCTYPE html>
<html>
<head>
    <title>Example</title>
    <script type="text/javascript">
        var numbers = [1,2,3,4,5,4,3,2,1]; 
        
        var mapResult = numbers.map(function(item, index, array){ 
            return item * 2; 
        }); 
        document.writeln(mapResult); //[2,4,6,8,10,8,6,4,2] 
       
    </script>
</head>
<body>
</body>
</html>

Click to view the demo

map() does not change the values contained in the array.