Document.caretRangeFromPoint()

The caretRangeFromPoint() method of the Document interface returns a Range object for the document fragment under the specified coordinates.

var range = document.caretRangeFromPoint(float x, float y);

x

A horizontal position within the current viewport.

y

A vertical position within the current viewport.

One of the following:

• A Range.
• Null, if x or y are negative, outside viewport, or there is no text entry node.

Basic demo: When clicking in a paragraph insert a line break at the caret position:

<p>Lorem ipsum dolor sit amet, consetetur sadipscing elitr,
sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat,
sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum.
Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.</p>

function insertBreakAtPoint(e) {
  let range;
  let textNode;
  let offset;

  if (document.caretPositionFromPoint) {
    range = document.caretPositionFromPoint(e.clientX, e.clientY);
    textNode = range.offsetNode;
    offset = range.offset;
  } else if (document.caretRangeFromPoint) {
    range = document.caretRangeFromPoint(e.clientX, e.clientY);
    textNode = range.startContainer;
    offset = range.startOffset;
  }
  // Only split TEXT_NODEs
  if (textNode && textNode.nodeType == 3) {
    let replacement = textNode.splitText(offset);
    let br = document.createElement('br');
    textNode.parentNode.insertBefore(br, replacement);
  }
}

let paragraphs = document.getElementsByTagName("p");
for (let i = 0; i < paragraphs.length; i++) {
  paragraphs[i].addEventListener('click', insertBreakAtPoint, false);
}