$("#loader").toggleClass('fadeOut',600).promise().done(function(){
    alert('a');
});

http://stackoverflow.com/questions/10321393/jquery-function-on-toggleclass-complete

How can I do a function once a toggleClass has completed? 

The .toggleClass method along with all other animation methods return a deferred object that you can access using .promise(). At that point, you can bind to it's done method.

jQuery - Function on toggleClass complete

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