Some utilities for detecting the caret position inside a contenteditable element

contenteditable-caret-position.js

/**
 * Get the number of characters in an element
 *
 * @param {Element} element
 * @return {number}
 */
function getTextLength(element) {
  let range = element.ownerDocument.createRange()
  range.selectNodeContents(element)

  return range.toString().length
}

/**
 * Get the character offset the caret is currently at
 *
 * @param {Element} element
 * @return {number}
 */
function getCaretOffset(element) {
  let sel = element.ownerDocument.defaultView.getSelection()
  if (sel.rangeCount === 0) return 0

  let range = element.ownerDocument.defaultView.getSelection().getRangeAt(0)
  let preCaretRange = range.cloneRange()
  preCaretRange.selectNodeContents(element)
  preCaretRange.setEnd(range.endContainer, range.endOffset)
  return preCaretRange.toString().length
}

/**
 * Check if the caret is at the start of an element
 * Returns `false` when the caret is part of a selection
 *
 * @param {Element} element
 * @return {boolean}
 */
function isCaretAtStart(element) {
  if (element.ownerDocument.activeElement !== element) return false
  if (
    element.ownerDocument.defaultView.getSelection().getRangeAt(0).toString()
      .length > 0
  )
    return false

  return getCaretOffset(element) === 0
}

/**
 * Check if the caret is at the end of an element
 * Returns `false` when the caret is part of a selection
 *
 * @param {Element} element
 * @return {boolean}
 */
function isCaretAtEnd(element) {
  if (element.ownerDocument.activeElement !== element) return false
  if (
    element.ownerDocument.defaultView.getSelection().getRangeAt(0).toString()
      .length > 0
  )
    return false

  return getCaretOffset(element) === getTextLength(element)
}

/**
 * Check if the caret is on the first line of an element
 * Returns `false` when the caret is part of a selection
 *
 * @param {Element} element
 * @return {boolean}
 */
function isCaretOnFirstLine(element) {
  if (element.ownerDocument.activeElement !== element) return false

  // Get the client rect of the current selection
  let window = element.ownerDocument.defaultView
  let selection = window.getSelection()
  if (selection.rangeCount === 0) return false

  let originalCaretRange = selection.getRangeAt(0)

  // Bail if there is text selected
  if (originalCaretRange.toString().length > 0) return false

  let originalCaretRect = originalCaretRange.getBoundingClientRect()

  // Create a range at the end of the last text node
  let startOfElementRange = element.ownerDocument.createRange()
  startOfElementRange.selectNodeContents(element)

  // The endContainer might not be an actual text node,
  // try to find the last text node inside
  let startContainer = startOfElementRange.endContainer
  let startOffset = 0
  while (startContainer.hasChildNodes() && !(startContainer instanceof Text)) {
    startContainer = startContainer.firstChild
  }

  startOfElementRange.setStart(startContainer, startOffset)
  startOfElementRange.setEnd(startContainer, startOffset)
  let endOfElementRect = startOfElementRange.getBoundingClientRect()

  return originalCaretRect.top === endOfElementRect.top
}

/**
 * Check if the caret is on the last line of an element
 * Returns `false` when the caret is part of a selection
 *
 * @param {Element} element
 * @return {boolean}
 */
function isCaretOnLastLine(element) {
  if (element.ownerDocument.activeElement !== element) return false

  // Get the client rect of the current selection
  let window = element.ownerDocument.defaultView
  let selection = window.getSelection()
  if (selection.rangeCount === 0) return false

  let originalCaretRange = selection.getRangeAt(0)

  // Bail if there is a selection
  if (originalCaretRange.toString().length > 0) return false

  let originalCaretRect = originalCaretRange.getBoundingClientRect()

  // Create a range at the end of the last text node
  let endOfElementRange = document.createRange()
  endOfElementRange.selectNodeContents(element)

  // The endContainer might not be an actual text node,
  // try to find the last text node inside
  let endContainer = endOfElementRange.endContainer
  let endOffset = 0
  while (endContainer.hasChildNodes() && !(endContainer instanceof Text)) {
    endContainer = endContainer.lastChild
    endOffset = endContainer.length ?? 0
  }

  endOfElementRange.setEnd(endContainer, endOffset)
  endOfElementRange.setStart(endContainer, endOffset)
  let endOfElementRect = endOfElementRange.getBoundingClientRect()

  return originalCaretRect.bottom === endOfElementRect.bottom
}

Hey @loilo,
is it ok if I use this code in one of my open source projects?

btw. here is an TS adjusted version I quickly created:

// Some utilities for detecting the caret position inside a contenteditable element

/**
 * Get the number of characters in an element
 */
export function getTextLength(element: HTMLElement) {
  let range = element.ownerDocument.createRange();
  range.selectNodeContents(element);

  return range.toString().length;
}

/**
 * Get the character offset the caret is currently at
 */
export function getCaretOffset(element: HTMLElement) {
  let sel = element.ownerDocument.defaultView?.getSelection();

  if (!sel || sel.rangeCount === 0) return 0;

  let range = element.ownerDocument.defaultView?.getSelection()?.getRangeAt(0);

  if (!range) return 0;

  let preCaretRange = range.cloneRange();

  preCaretRange.selectNodeContents(element);
  preCaretRange.setEnd(range.endContainer, range.endOffset);

  return preCaretRange.toString().length;
}

/**
 * Check if the caret is at the start of an element
 * Returns `false` when the caret is part of a selection
 */
export function isCaretAtStart(element: HTMLElement) {
  if (element.ownerDocument.activeElement !== element) return false;

  const caretRange = element.ownerDocument.defaultView
    ?.getSelection()
    ?.getRangeAt(0)
    .toString();

  if (!caretRange || caretRange.length > 0) return false;

  return getCaretOffset(element) === 0;
}

/**
 * Check if the caret is at the end of an element
 * Returns `false` when the caret is part of a selection
 */
export function isCaretAtEnd(element: HTMLElement) {
  if (element.ownerDocument.activeElement !== element) return false;

  const caretRange = element.ownerDocument.defaultView
    ?.getSelection()
    ?.getRangeAt(0)
    .toString();

  if (!caretRange || caretRange.length > 0) return false;

  return getCaretOffset(element) === getTextLength(element);
}

/**
 * Check if the caret is on the first line of an element
 * Returns `false` when the caret is part of a selection
 */
export function isCaretOnFirstLine(element: HTMLElement) {
  if (element.ownerDocument.activeElement !== element) return false;

  // Get the client rect of the current selection
  let selection = element.ownerDocument.defaultView?.getSelection();
  if (!selection || selection.rangeCount === 0) return false;

  let originalCaretRange = selection.getRangeAt(0);

  // Bail if there is text selected
  if (originalCaretRange.toString().length > 0) return false;

  let originalCaretRect = originalCaretRange.getBoundingClientRect();

  // Create a range at the end of the last text node
  let startOfElementRange = element.ownerDocument.createRange();
  startOfElementRange.selectNodeContents(element);

  // The endContainer might not be an actual text node,
  // try to find the last text node inside
  let startContainer = startOfElementRange.endContainer;
  let startOffset = 0;

  while (startContainer.hasChildNodes() && !(startContainer instanceof Text)) {
    if (!startContainer.firstChild) continue;

    startContainer = startContainer.firstChild;
  }

  startOfElementRange.setStart(startContainer, startOffset);
  startOfElementRange.setEnd(startContainer, startOffset);
  let endOfElementRect = startOfElementRange.getBoundingClientRect();

  return originalCaretRect.top === endOfElementRect.top;
}

/**
 * Check if the caret is on the last line of an element
 * Returns `false` when the caret is part of a selection
 */
export function isCaretOnLastLine(element: HTMLElement) {
  if (element.ownerDocument.activeElement !== element) return false;

  // Get the client rect of the current selection
  let window = element.ownerDocument.defaultView;

  if (!window) return false;

  let selection = window.getSelection();

  if (!selection || selection.rangeCount === 0) return false;

  let originalCaretRange = selection.getRangeAt(0);

  // Bail if there is a selection
  if (originalCaretRange.toString().length > 0) return false;

  let originalCaretRect = originalCaretRange.getBoundingClientRect();

  // Create a range at the end of the last text node
  let endOfElementRange = document.createRange();
  endOfElementRange.selectNodeContents(element);

  // The endContainer might not be an actual text node,
  // try to find the last text node inside
  let endContainer = endOfElementRange.endContainer;
  let endOffset = 0;

  while (endContainer.hasChildNodes() && !(endContainer instanceof Text)) {
    if (!endContainer.lastChild) continue;

    endContainer = endContainer.lastChild;
    endOffset = (endContainer as Text).length ?? 0;
  }

  endOfElementRange.setEnd(endContainer, endOffset);
  endOfElementRange.setStart(endContainer, endOffset);
  let endOfElementRect = endOfElementRange.getBoundingClientRect();

  return originalCaretRect.bottom === endOfElementRect.bottom;
}

Hey @ErfanEbrahimnia, sure, go for it!
(I have noted licensing information for my gists here, just FYI.)

Thank you ❤️

Bro i am impresive how legend you are

Thank you so much!

I was wondering why sometime you get the selection with element.ownerDocument.defaultView?.getSelection() and sometime with window.getSelection...

@benoitlahoz I always use element.ownerDocument.defaultView, I just sometimes do let window = element.ownerDocument.defaultView before. In retrospect thoguh, I agree that this was a terrible design decision for reading the code later. 😅