.delay() and .setTimeout()

According to jQuery document on .delay(),

The .delay() method is best for delaying between queued jQuery effects. Because it is limited—it doesn't,开发者_如何转开发 for example, offer a way to cancel the delay—.delay() is not a replacement for JavaScript's native setTimeout function, which may be more appropriate for certain use cases.

Could someone please expand on this? When is it more appropriate to use .delay(), and when is it better to use .setTimeout()?

I think what you posted explains itself really.

Use .delay() for jQuery effects including animations.

setTimeout() is best used for everything else. For example when you need to trigger an event at a certain elapsed time.

As far as I understand, .delay() is meant specifically for adding a delay between methods in a given jQuery queue. For example, if you wanted to fade an image into view during the span of 1 second, have it visible for 5 seconds, and then spend another second to fade it out of view again, you could do the following:

$('#image').fadeIn(1000).delay(5000).fadeOut(1000);

In this instance, .delay() is more intuitive to use since it is specifically meant for delaying events in a given jQuery queue. setImeout(), on the other hand, is a native JavaScript method that isn't intended explicitly for a queue line. If you wanted an alert box to pop up 1 second after clicking on a button, you could do the following:

function delayAlert() {
    var x = setTimeout("alert('5 seconds later!')", 5000);
}

<input type="submit" value="Delay!" onclick="delayAlert();" />

You can use delay with animations, for example:

$('.message').delay(5000).fadeOut();

You can also use timeOut to delay the start of animations, for example:

window.setTimeout(function(){
  $('.message').fadeOut();
}, 5000);

As you see, it's easier to use delay than setTimeout with animations.

You can delay pretty much anything with setTimeout, but you can only delay animations with delay. Methods that aren't animations are not affected by delay, so this would not wait a while before hiding the element, it would hide it immediately:

$('.message').delay(5000).hide();

.delay() is mostly used for chaining together animation effects with pauses in between.

As the docs mention, there is no way to cancel the delay. In the case where you may want to cancel the delay, a setTimeout() should be used instead so you can cancel it with clearTimeout()

Another side effect of delay(): it seems to disable the ability to hide (or fadeOut, etc) the objecting being delayed, until the delay is over.

For example, I set up the following code (perhaps a stackoverflow developer will recognize the css names....) to hide a 'div':

 $j(document).ready(function(){
   var $messageDiv = $j("<div>").addClass('fading_message')
       .text("my alert message here").hide();
   var $closeSpan = $j("<span>").addClass('notify_close').text("x");
   $closeSpan.click(function() {$j(this).parent().slideUp(400);});
   $messageDiv.append($closeSpan);
   $j('.content_wrapper_div').prepend($messageDiv);
   $messageDiv.fadeTo(500, .9).delay(5000).fadeTo(800,0);
 });

Clicking the "x" that's in the span (that's in the 'div') did fire off the click function (I tested with an alert in there), but the div didn't slideUp as directed. However, If I replace the last line with this:

     $messageDiv.fadeTo(500, .9);

..then it did work - when I clicked the "x", the surrounding div slideUp and and away. It seems as if the background running of the "delay()" function on the $messageDiv "locked" that object, so that a separate mechanism trying to close it couldn't do so until the delay was done.