Created attachment 400093 [details]
A video demonstrating the bug

Overview:

In Safari 13.1 on macOS 10.14 and 10.15, setting a TEXTAREA's value through Javascript and deleting lines from the middle to the top with the DELETE/BACKSPACE key doesn't remove empty lines. This doesn't occur on any other browser tested (Chrome, Firefox, Opera, Brave, Edge).

Steps to Reproduce:

1. Navigate to the test case at: https://jsfiddle.net/d75xzjg0/3/

2. Insert the cursor on the empty line between 3 and 4.

3. Type DELETE/BACKSPACE six types to remove the lines for 3, 2, and 1.

Actual Result:

The text is removed but the empty lines remain. The position of the lines for 4, 5, and 6 do not change.

Expected Result:

We expect the newly empty lines to be removed with DELETE/BACKSPACE, so the lines for 4, 5, and 6 are pulled up to the top of the TEXTAREA. This is the behavior on other browsers, and the behavior of Safari prior to 13.1.

Notes:

I've attached a video demonstrating the issue.

If the jsFiddle is unavailable, the code to reproduce is:

~~~
<textarea rows="20" cols="50"></textarea>

<script type="text/javascript">
var sel = document.querySelector('textarea');

sel.value = "1\n2\n3\n\n4\n5\n6\n";
</script>
~~~

The issue occurs whether the newlines of the inserted text are CRLF or LF.

The issue also persists whether or not there is default text in the TEXTAREA.