Thursday, 27 June 2013

jQuery.each() function


jQuery.each( collection, callback(indexInArray, valueOfElement) ) Returns: Object


Description: A generic iterator function, which can be used to seamlessly iterate over both objects and arrays. Arrays and array-like objects with a length property (such as a function's arguments object) are iterated by numeric index, from 0 to length-1. Other objects are iterated via their named properties.

jQuery.each( collection, callback(indexInArray, valueOfElement) )
collectionThe object or array to iterate over.
callback(indexInArray, valueOfElement)The function that will be executed on every object.

The $.each() function is not the same as $(selector).each(), which is used to iterate, exclusively, over a jQuery object. The $.each() function can be used to iterate over any collection, whether it is a map (JavaScript object) or an array. In the case of an array, the callback is passed an array index and a corresponding array value each time. (The value can also be accessed through the this keyword, but Javascript will always wrap the this value as an Object even if it is a simple string or number value.) The method returns its first argument, the object that was iterated.


$.each([52, 97], function(index, value) { 
  alert(index + ': ' + value); 
});

This produces two messages:
0: 52
1: 97

If a map is used as the collection, the callback is passed a key-value pair each time:

var map = { 
  'flammable': 'inflammable', 
  'duh': 'no duh' 
}; 
$.each(map, function(key, value) { 
  alert(key + ': ' + value); 
});

Once again, this produces two messages:
flammable: inflammable
duh: no duh

We can break the $.each() loop at a particular iteration by making the callback function return false. Returning non-false is the same as a continue statement in a for loop; it will skip immediately to the next iteration.

Examples:

Example: Iterates through the array displaying each number as both a word and numeral

<!DOCTYPE html>
<html>
<head>
  <style>
  div { color:blue; }
  div#five { color:red; }
  </style>
  <script src="http://code.jquery.com/jquery-latest.js"></script>
</head>
<body>
  
  <div id="one"></div>
  <div id="two"></div>
  <div id="three"></div>
  <div id="four"></div>
  <div id="five"></div>
<script>
    var arr = [ "one", "two", "three", "four", "five" ];
    var obj = { one:1, two:2, three:3, four:4, five:5 };

    jQuery.each(arr, function() {
      $("#" + this).text("Mine is " + this + ".");
       return (this != "three"); // will stop running after "three"
   });

    jQuery.each(obj, function(i, val) {
      $("#" + i).append(document.createTextNode(" - " + val));
    });
</script>
</body>
</html>
 
DEMO:
Mine is one. - 1
Mine is two. - 2
Mine is three. - 3
-4
-5



Example: Iterates over the properties in an object, accessing both the current item and its key.
$.each( { name: "John", lang: "JS" }, function(k, v){
   alert( "Key: " + k + ", Value: " + v );
 });

Example: Iterates over items in an array, accessing both the current item and its index.

$.each( ['a','b','c'], function(i, l){
   alert( "Index #" + i + ": " + l );
 });

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