javascript - In jQuery, is it faster to check if an element exists before trying to bind event handlers? - Stack Overflow

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Is it faster to first check if an element exists, and then bind event handlers, like this:

if( $('.selector').length ) {
    $('.selector').on('click',function() {
          // Do stuff on click
    }
}

or is it better to simply do:

$('.selector').on('click',function() {
     // Do stuff on click
}

All this happens on document ready, so the less delay the better.

Is it faster to first check if an element exists, and then bind event handlers, like this:

if( $('.selector').length ) {
    $('.selector').on('click',function() {
          // Do stuff on click
    }
}

or is it better to simply do:

$('.selector').on('click',function() {
     // Do stuff on click
}

All this happens on document ready, so the less delay the better.

• javascript
• jquery
• performance

Share Improve this question Follow asked Feb 24, 2014 at 13:40 NiclasNiclas 1,40211 gold badge1212 silver badges2525 bronze badges 6

• 4 if( $('.selector').length ) { $('.selector').on('click',function() { // Do stuff on click } } will be much slower because the selector is evaluated twice.... if you cache it I don't think it will make much difference – Arun P Johny Commented Feb 24, 2014 at 13:41
• possible duplicate of should I test whether a target element exists before I bind a function to it? – Tjkoopa Commented Feb 24, 2014 at 13:43
• If it were faster, there would be a test at the beginning of the function. And adding such a test hindering readability for unmeasured performance gains before profiling would be a case of very premature optimization. – Denys Séguret Commented Feb 24, 2014 at 13:43
• 2 $('.selector').on('click',function() { // Do stuff on click } will bind if element exists otherwise not. So this is faster. – Bharadwaj Commented Feb 24, 2014 at 13:43
• @Bharadwaj You could add your comment as an answer. – Harry Dobrev Commented Feb 24, 2014 at 13:47

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4 Answers 4

Sorted by: Reset to default 13

A better way to write the if check is like this

var elems = $('.selector');
if( elems.length ) {
    elems.on('click',function() {
          // Do stuff on click
    });
}

So let us test this and see what the code tells us http://jsperf.com/speed-when-no-matches

In the end you are talking milliseconds of difference and the non if check is not going to be noticeable when run once. This also does not take into account when there are elements to find, than in that case, there is an extra if check. Will that check matter

So let us look when they find elements http://jsperf.com/speed-when-has-matches

There is really no difference. So if you want to save fractions of a millisecond, do the if. If you want more compact code, than leave it the jQuery way. In the end it does the same thing.

Just use

$('.selector').on('click',function() {
     // Do stuff on click
}

If no elements exist with the class selector, jQuery will simply not bind anything.

$('.selector').on('click',function() { // Do stuff on click } will bind if element exists otherwise not. So this is faster.

Use the binding directly.

$('selector').on('click',function() {
    // Do stuff on click
}

If if there are no elements with the specified selector, it won't do anything - not even post an error, which means that actual check for the element would be doing the same thing twice. I wouldn't call it exactly a check of the existence of an element, but the way this is implemented in jQuery certainly acts that way.

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