Posted in: Performance

Don’t Act on Absent Elements

jQuery won't tell you if you're trying to run a whole lot of code on an empty selection – it will proceed as though nothing's wrong. It's up to you to verify that your selection contains some elements.

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// Bad: This runs three functions before it
// realizes there's nothing in the selection
$( "#nosuchthing" ).slideUp();
 
// Better:
var elem = $( "#nosuchthing" );
 
if ( elem.length ) {
 
    elem.slideUp();
 
}
 
// Best: Add a doOnce plugin.
jQuery.fn.doOnce = function( func ) {
 
    this.length && func.apply( this );
 
    return this;
 
}
 
$( "li.cartitems" ).doOnce(function() {

 
    // make it ajax! \o/

 
});

This guidance is especially applicable for jQuery UI widgets, which have a lot of overhead even when the selection doesn't contain elements.