If your are going to specify an animate callback that
executes when animate is complete, then you must specify an
easing value. This property is not optional with zepto js but
it is in jquery. If you do not care about easing, just set this
value to null as in the example below
$('#myImage').animate({'opacity':'0'}, 5000, null, function(){
alert('complete');
});
See also
Use your Android as a Genie garage door opener remote