Contenteditable DIV - how can I determine if the cursor is at the start or end of the content

Question

I have a contenteditable div which contains typical wysiwyg editor html (bold, anchors, lists).

I need to determine if the current cursor is, onKeyDown, at the start

Answer 1

This is how I ended up solving this. My proposed solution above worked sometimes but there were way to many edge cases, so I ended up considering how much text was before or after the cursor, and if that was 0 characters, then I was at the start or end:

handle_keydown = function(e) {
  // Get the current cusor position
  range = window.getSelection().getRangeAt(0)
  // Create a new range to deal with text before the cursor
  pre_range = document.createRange();
  // Have this range select the entire contents of the editable div
  pre_range.selectNodeContents(this);
  // Set the end point of this range to the start point of the cursor
  pre_range.setEnd(range.startContainer, range.startOffset);
  // Fetch the contents of this range (text before the cursor)
  this_text = pre_range.cloneContents();
  // If the text's length is 0, we're at the start of the div.
  at_start = this_text.textContent.length === 0;
  // Rinse and repeat for text after the cursor to determine if we're at the end.
  post_range = document.createRange();
  post_range.selectNodeContents(this);
  post_range.setStart(range.endContainer, range.endOffset);
  next_text = post_range.cloneContents();
  at_end = next_text.textContent.length === 0;
}

Still not entirely sure there are any other edge cases, as I'm not entirely sure how to unit test this, since it requires mouse interaction - there's probably a library to deal with this somewhere.