Description

It appears that if I trigger a blur event, immediately after an alert() inside a click event handler, it results in an error:

Uncaught TypeError: saved.slice is not a function

This is happening in jQuery 3.7.1 and 4.0.0-beta. But not in 3.5.1. I wonder if this issue might be related.

Link to test case

The way to reproduce this is quite simple:

    $('button').on('click', function (e) {
      alert('Hello');
      
      $(this).trigger('blur');
    })

https://jsbin.com/vuquzepidi/edit?html%2Cjs%2Coutput=

I've found that if I use console.log instead of alert() it works just fine. Also if I put the trigger into a setTimeout it works just fine. Likewise if I change it to trigger a focus event it works. I did try a focus before the blur, wondering if the alert might cause the button to loose focus, but no change, and even if it did, I would have expected an error.

Apologies, I haven't yet dug into the code to see what might be happening - I can see in the debugger that saved is true, but I've not looked to see why that is yet.