how to compare two elements in jquery

Question

var a=$('#start > div:last-child');
var b=$('#start > div.live')[0];
alert(a==b)
alert(a==$(b))

It's always false. How can you compare two elements in jQuery?

thanks

Answer 1

For the record, jQuery has an is() function for this:

a.is(b)

Note that a is already a jQuery instance.

Answer 2

You could compare DOM elements. Remember that jQuery selectors return arrays which will never be equal in the sense of reference equality.

Assuming:

<div id="a" class="a"></div>

this:

$('div.a')[0] == $('div#a')[0]

returns true.

Answer 3

Every time you call the jQuery() function, a new object is created and returned. So even equality checks on the same selectors will fail.

<div id="a">test</div>

$('#a') == $('#a') // false

The resulting jQuery object contains an array of matching elements, which are basically native DOM objects like HTMLDivElement that always refer to the same object, so you should check those for equality using the array index as Darin suggested.

$('#a')[0] == $('#a')[0] // true

Answer 4

a.is(b)

and to check if they are not equal use

!a.is(b)

as for

$b = $('#a')
....
$('#a')[0] == $b[0] // not always true

maybe class added to the element or removed from it after the first assignment

Answer 5

Random AirCoded example of testing "set equality" in jQuery:

$.fn.isEqual = function($otherSet) {
  if (this === $otherSet) return true;
  if (this.length != $otherSet.length) return false;
  var ret = true;
  this.each(function(idx) { 
    if (this !== $otherSet[idx]) {
       ret = false; return false;
    }
  });
  return ret;
};

var a=$('#start > div:last-child');
var b=$('#start > div.live')[0];

console.log($(b).isEqual(a));

Answer 6

The collection results you get back from a jQuery collection do not support set-based comparison. You can use compare the individual members one by one though, there are no utilities for this that I know of in jQuery.