What causes the unexpected behavior of JQuery's .animate() function?

Question

What causes the unexpected behavior of JQuery's .animate() function?

I am currently working on a project that involves creating a div element for the purpose of dragging and dropping files. My goal is to have the height of the div increase when a file is dragged into it, and decrease when the file is dragged out.

To achieve this functionality, I have implemented event listeners for the 'ondragover' and 'ondragleave' events, along with utilizing the .css() function to adjust the height of the div. While everything works as intended using the .css() function, I encountered unexpected behavior when attempting to use the .animate() function. When dragging over the div, the height increases as expected, but if the file is then dragged out without being dropped, the height does not decrease as desired.

Feel free to experiment below by dragging a file in and out of the div without actually dropping it:


            function enter_drop(){
                $("#box").animate({height: "300px"}, 500);
            }

            function leave_drop(){
                $("#box").animate({height: "100px"}, 500);
            }


            <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
            
            <div id="box" style="background:#98bf21;height:100px;width:100px;margin:6px;float:left" ondragover="enter_drop()" ondragleave="leave_drop()"></div>

            <img id="drag1" src="http://cdn.sstatic.net/Sites/stackoverflow/img/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="234253534f460e574c56404b0e4a404c4d63110d534d44">[email protected]</a>" draggable="true" style="float:left">

javascript jquery html css

Answer 1

Answer №1

The ondragover event is triggered continuously while an element is dragged over a drop target.

When using jQuery's .animate() function, each callback is queued up. This means that when you trigger the ondragleave event, there may still be animations running in the background.

To stop and immediately execute any pending animations, you can use the .stop(true) method to clear the animation queue.

function enter_drop(e){
  $("#box").animate({height: "300px"},500);
}

function leave_drop(e){
  $("#box").stop(true).animate({height: "100px"},500);
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>


<div id="box" style="background:#98bf21;height:100px;width:100px;margin:6px;" ondragover="enter_drop()" ondragleave="leave_drop()"></div>

<img id="drag1" src="http://cdn.sstatic.net/Sites/stackoverflow/img/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="99f8e9e9f5fcb4edf6ecfaf1b4f0faf6f7d9abb7e9f7fe">[protected]</a>" style="width:50px;height:50px;" draggable="true">

Answer 2

The ondragover event is triggered continuously while an element is dragged over a drop target.

When using jQuery's .animate() function, each callback is queued up. This means that when you trigger the ondragleave event, there may still be animations running in the background.

To stop and immediately execute any pending animations, you can use the .stop(true) method to clear the animation queue.

function enter_drop(e){
  $("#box").animate({height: "300px"},500);
}

function leave_drop(e){
  $("#box").stop(true).animate({height: "100px"},500);
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>


<div id="box" style="background:#98bf21;height:100px;width:100px;margin:6px;" ondragover="enter_drop()" ondragleave="leave_drop()"></div>

<img id="drag1" src="http://cdn.sstatic.net/Sites/stackoverflow/img/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="99f8e9e9f5fcb4edf6ecfaf1b4f0faf6f7d9abb7e9f7fe">[protected]</a>" style="width:50px;height:50px;" draggable="true">

Answer 3

Answer №2

It has been noted that @Cue's response correctly identifies the root cause of the issue.

Nevertheless, resorting to .stop(true) in order to halt an excessively drawn-out animation queue is not the optimal resolution. A more effective strategy involves triggering your animation only once on ondragenter.

In reality, a combination of both methods works best:

Initiate enter_drop just once on ondragenter…
and utilize .stop(true).animate(... on ondragleave, ensuring that if the initial animation is still ongoing when leaving, the element won't resume the enter animation but rather come to a standstill at its current height position before animating back towards 100.

function enter_drop(){
  $("#box").animate({height: 300},350);
}

function leave_drop(){
  $("#box").stop(true).animate({height: 100},350);
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>


<div id="box" style="background:#98bf21;height:100px;width:100px;margin:6px;float:left" ondragenter="enter_drop()" ondragleave="leave_drop()"></div>

<img id="drag1" src="http://cdn.sstatic.net/Sites/stackoverflow/img/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="d2b3a2a2beb7ffa6bda7b1baffbbb1bdbc92e0fca2bcb5">[email protected]</a>" draggable="true" style="width: 100px;">

Answer 4

It has been noted that @Cue's response correctly identifies the root cause of the issue.

Nevertheless, resorting to .stop(true) in order to halt an excessively drawn-out animation queue is not the optimal resolution. A more effective strategy involves triggering your animation only once on ondragenter.

In reality, a combination of both methods works best:

Initiate enter_drop just once on ondragenter…
and utilize .stop(true).animate(... on ondragleave, ensuring that if the initial animation is still ongoing when leaving, the element won't resume the enter animation but rather come to a standstill at its current height position before animating back towards 100.

function enter_drop(){
  $("#box").animate({height: 300},350);
}

function leave_drop(){
  $("#box").stop(true).animate({height: 100},350);
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>


<div id="box" style="background:#98bf21;height:100px;width:100px;margin:6px;float:left" ondragenter="enter_drop()" ondragleave="leave_drop()"></div>

<img id="drag1" src="http://cdn.sstatic.net/Sites/stackoverflow/img/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="d2b3a2a2beb7ffa6bda7b1baffbbb1bdbc92e0fca2bcb5">[email protected]</a>" draggable="true" style="width: 100px;">

What causes the unexpected behavior of JQuery's .animate() function?

Answer №1

Answer №2

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