Document: caretPositionFromPoint() 方法

caretPositionFromPoint(x, y)

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) {
    // Use WebKit-proprietary fallback method
    range = document.caretRangeFromPoint(e.clientX, e.clientY);
    textNode = range.startContainer;
    offset = range.startOffset;
  } else {
    // Neither method is supported, do nothing
    return;
  }
  // Only split TEXT_NODEs
  if (textNode?.nodeType === 3) {
    let replacement = textNode.splitText(offset);
    let br = document.createElement("br");
    textNode.parentNode.insertBefore(br, replacement);
  }
}

let paragraphs = document.getElementsByTagName("p");
for (const paragraph of paragraphs) {
  paragraph.addEventListener("click", insertBreakAtPoint, false);
}

let message = document.getElementById("message");
if (document.caretPositionFromPoint) {
  message.textContent =
    "This browser supports the standard document.caretPositionFromPoint";
  message.classList.add("supported");
} else if (document.caretRangeFromPoint) {
  message.textContent =
    "This browser supports the non-standard document.caretRangeFromPoint";
  message.classList.add("supported");
}

<div id="message">
  This browser supports neither document.caretRangeFromPoint nor
  document.caretPositionFromPoint
</div>

<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>

#message {
  color: red;
  font-weight: bold;
}

#message.fallback {
  color: darkorange;
}

#message.supported {
  color: green;
}