javascript.map.js

//Explaning call in map 

Using map generically

This example shows how to use map on a String to get an array of bytes in the ASCII encoding representing the character values:

var map = Array.prototype.map;
var a = map.call('Hello World', function(x) { 
  return x.charCodeAt(0); 
});
// a now equals [72, 101, 108, 108, 111, 32, 87, 111, 114, 108, 100]
Using map generically querySelectorAll

This example shows how to iterate through a collection of objects collected by querySelectorAll. In this case we get all selected options on the screen and printed on the console:

var elems = document.querySelectorAll('select option:checked');
var values = Array.prototype.map.call(elems, function(obj) {
  return obj.value;
});
Using map to reverse a string

var str = '12345';
Array.prototype.map.call(str, function(x) {
  return x;
}).reverse().join(''); 

// Output: '54321'
// Bonus: use '===' to test if original string was a palindrome