Perf.printWasted prints newly inserted dom nodes in list as a waste of time

[slorber]

First of all, during my attempt to show you this bug, I found this weird behavior:

1. http://jsfiddle.net/kb3gN/4092/ does not show any time wasted (on user click action)
2. http://jsfiddle.net/kb3gN/4093/ does
   I don't know why one does show wasted time and not the other

On 2) I use shouldComponentUpdate=true, and we can see the time waste grows with the list size as well as the number of instances in the table.

So finally, to demonstrate my problem, see http://jsfiddle.net/kb3gN/4094/
I've implemented correctly shouldComponentUpdate and now each time I add a new element in the list, it is considered as a waste of time. My table always show 1 instance: the one that just got inserted.

I've had this problem on my app, when dealing with a paginated list (loading more items from the server as the user scrolls down). I don't think this newly inserted node should be printed in printWasted

[zpao]

@petehunt is on vacation right now but hopefully he'll have a chance to chime in when he gets back. @josh might be able to help out too if he's around.

[sophiebits]

Probably @joshduck. :)

[zpao]

Oops, sorry Josh! If you want to send some GH staff over to help debug though…

[sophiebits]

Curiously, this seems inconsistent if I leave the (third) page open and just watch it update:

[slorber]

Yes I've seen something like that too @spicyj ! but for my real app it seems to print the table constantly.
Maybe the inserted node is considered a waste but sometimes it works fine and it is not...

[jeffchan]

Running into same issue here #2105
Inconsistently in the reproduction, consistently in my own app as well.

[bobbyrenwick]

👍 having the same issue!

[koba04]

I suppose it's because setProps is batch update.
You should print in callback.

    component.setProps({state: state}, function() {
        React.addons.Perf.stop();
        React.addons.Perf.printWasted();
    });

The fixed fiddles are below.

• http://jsfiddle.net/koba04/5st9eaur/1/
• http://jsfiddle.net/koba04/0dhpegsh/

Unfortunately, totalTime is still incorrect...
#3436

[slorber]

thanks @koba04 will try that.

Also I linked a related question, can you take a look? #3611