Performance issue in the dragover event of the dndLists directive.

[johntdowney]

Hey, just leaving this here for the author and/or those who care because I spent a little while solving this issue while working with a very large drag and drop list.

Line 339/340 is as follows:

listNode.insertBefore(placeholderNode,
	isFirstHalf ? listItemNode : listItemNode.nextSibling);

Replacing these two lines with

if(isFirstHalf) {
	if(listItemNode.previousSibling != placeholderNode) listNode.insertBefore(placeholderNode, listItemNode);
} else {
	if(listItemNode.nextSibling != placeholderNode) listNode.insertBefore(placeholderNode, listItemNode.nextSibling);
}

dramatically cuts down on the number of DOM layouts and improves the execution time of the dragover event handler. Without this, it's pretty hobbled at around ~60 dnd list items.

Thanks,
John Downey

[tagisen]

amazing job @johntdowney
I had a short list to work with, but with complex moving item. Replacing those lines did the magic. Thanks

[GeorgeChackungal]

Awesome Job! Can Someone add it into the original source?

[johntdowney]

Glad I could help! I see this "Close and comment" button, but I'm not sure of the etiquette here regarding whether or not I should close this issue since I opened it, so I'll just hit the comment button instead and assume someone with more authority can close it once the change has been applied.

[orlandovallejos]

@marceljuenemann please review the PR, and run the minifier.

[sinzii]

Awesome! Thank you so much, that improve a lot than the original.

[abtx]

Fantastic, thanks @johntdowney ! Has a PR been submitted for this fix?

[sagg629]

Thank you so much!
Now the drag procedure is much, much more smoothly, especially on a Mac PC with Chrome.

I would like this library to be updated more constantly, the last update is from 2017!

[Miki-AG]

You can improve performance a bit more by throttling:

      var throttle = true; 
      element.on('dragover', function(event) {
        if (throttle) {
          throttle = false;
          event = event.originalEvent || event;
          ...
          ent.addClass("dndDragover");
          event.stopPropagation();
          setTimeout(() => {
            throttle = true;
          }, 50);
        }
        return false;
      });

[royalone]

I also added some throttling, using lodash.
replacing line 310

element.on('dragover', function(event) {

with

element.on('dragover', _.throttle(dragOver, 50, { leading: true, trailing: false }))
function dragOver(event){

you'll also need to get rid of the extra bracket etc. at the end of the function