How to check null objects in jQuery

Question

I\'m using jQuery and I want to check the existence of an element in my page. I have written following code, but it\'s not working:

if($(\"#btext\" + i) != n         


        

Answer 1

Calling length property on undefined or a null object will cause IE and webkit browsers to fail!

Instead try this:

if($("#something") !== null){
  // do something
}

or

if($("#something") === null){
  // don't do something
}

Answer 2

when the object is empty return this error:

Uncaught TypeError: Cannot read property '0' of null

I try this code :

try{
  if ($("#btext" + i).length) {};               
}catch(err){
  if ($("#btext" + i).length) {
     //working this code if the item, not NULL 
   }
}

Answer 3

Check the jQuery FAQ...

You can use the length property of the jQuery collection returned by your selector:

if ( $('#myDiv').length ){}

Answer 4

(Since I don't seem to have enough reputation to vote down the answer...)

Wolf wrote:

Calling length property on undefined or a null object will cause IE and webkit browsers to fail!

Instead try this:

 // NOTE!! THE FOLLOWING IS WRONG; DO NOT USE!  -- EleotleCram
if($("#something") !== null){
  // do something
}

or

 // NOTE!! THE FOLLOWING IS WRONG; DO NOT USE!  -- EleotleCram
if($("#something") === null){
  // don't do something
}

While it is true that calling the length property on an undefined or null object will cause browsers to fail, the result of jQuery's selectors (the $('...')) will never be null or undefined. Thus the code suggestions make no sense. Use one of the other answers, they make more sense.

---

(Update 2012) Because people look at code and this answer is pretty high up the list: For the last couple of years, I have been using this small plugin:

  jQuery.fn['any'] = function() {
     return (this.length > 0);
  };

I think $('div').any() reads better than $('div').length, plus you won't suffer as much from typos: $('div').ayn() will give a runtime error, $('div').lenght will silently most likely always be falsy.

__
Edits november 2012:

1) Because people tend to look at code and not read what is said around the code, I added two big caveat lector notes to the quoted code of Wolf.
2) I added code of the small plugin I use for this situation.

Answer 5

jquery $() function always return non null value - mean elements matched you selector cretaria. If the element was not found it will return an empty array. So your code will look something like this -

if ($("#btext" + i).length){
        //alert($("#btext" + i).text());
    $("#btext" + i).text("Branch " + i);
}

Answer 6

In jQuery 1.4 you get the $.isEmptyObject function, but if you are forced to use an older version of jQ like us poor Drupal developers just steal use this code:

// This is a function similar to the jQuery 1.4 $.isEmptyObject.
function isObjectEmpty(obj) {
  for ( var name in obj ) {
    return false;
  }
  return true;
}

Use it like:

console.log(isObjectEmpty(the_object)); // Returns true or false.