We're setting caret position, when user changes threads. It enables us to load saved caret position when jumping between threads. We have to set both start and end of selection to the same number as we don't want any selected text at start.

We need to change caret position in textarea after we choose user to mention. Draft is edited (we paste remaining part of chosen username that wasn't typed previously). this.textarea.selectionStart === this.textarea.selectionEnd part of condition is there to prevent situation where we want to select some text, but first click (start of selection) sets inputState.textCursorPosition, second click sets it again and then both start and end are set in the code above. This way text selecting can work independently of mentioning other users. We can't merge it with previous if as they're serving different purposes and require different conditions. We might create util function to call instead of the whole block:

this.textarea?.setSelectionRange(
        inputState.textCursorPosition,
        inputState.textCursorPosition,
        'none',
      );

Currently not, as using keyboard was out of scope for this stack of diffs, but when we add it, we should probably refactor setting cursor to selectionStart as a separate function. We only do that on text change, clicks and choosing user (from list of users in overlay) to mention .

You're right, obviously, I think in some previous versions, codes inside were different, thus they needed to be separeted.

Sorry, I deleted that comment, as it was few years old, and that feature is already implemented. We only show send button, when draft is nonempty

I had some troubles with making it work earlier while working on it. Added onSelect event handler for textarea and it works now. We update state on user using arrows.