How to check whether an element exists with jQuery

When we using jQuery (or any other JavaScript library for that matter), have you ever wondered how to test whether an element exists using a selector? Well, maybe you haven't, but I have - lots of times - so I thought I'd share how it's done here because it's not as simple as it seems.

if ($("#div_id")){

  // code goes here

}

What's wrong - it will not work! When you use a selector, jQuery will always return an object. Therefore the if statement will always be true and never be false. In the case of an element that does not exist on the page, jQuery will return an object with nothing in it - an empty object.

With a jQuery selector we can also use the length property, which will return the size of the object. Do you see where I'm heading with this? That's right, lets just change our if statement to:

if ($("#div_id").length > 0){

  // code goes here

}

Now it works because when jQuery returns an empty object, the length property will return zero and therefore the if statement will be false.