HTML contenteditable: Keep Caret Position When Inner HTML Changes-CodePudding

I have a div that acts as a WYSIWYG editor. This acts as a text box but renders markdown syntax within it, to show live changes.

Problem: When a letter is typed, the caret position is reset to the start of the div.

const editor = document.querySelector('div');
editor.innerHTML = parse('**dlob**  *cilati*');

editor.addEventListener('input', () => {
  editor.innerHTML = parse(editor.innerText);
});

function parse(text) {
  return text
    .replace(/\*\*(.*)\*\*/gm, '**<strong>$1</strong>**')     // bold
    .replace(/\*(.*)\*/gm, '*<em>$1</em>*');                  // italic
}

div {
  height: 100vh;
  width: 100vw;
}

<div contenteditable />

Codepen: https://codepen.io/ADAMJR/pen/MWvPebK

Markdown editors like QuillJS seem to edit child elements without editing the parent element. This avoids the problem but I'm now sure how to recreate that logic with this setup.

Question: How would I get the caret position to not reset when typing?

CodePudding user response：

You need to keep the state of the position and restore it on each input. There is no other way. You can look at how content editable is handled in my project jQuery Terminal (the links point to specific lines in source code and use commit hash, current master when I've written this, so they will always point to those lines).

insert method that is used when user type something (or on copy-paste).
fix_textarea - the function didn't changed after I've added content editable. The function makes sure that textarea or contenteditable (that are hidden) have the same state as the visible cursor.
clip object (that is textarea or content editable - another not refactored name that in beginning was only for clipboard).

For position I use jQuery Caret that is the core of moving the cursor. You can easily modify this code and make it work as you want. jQuery plugin can be easily refactored into a function move_cursor.

This should give you an idea how to implement this on your own in your project.

CodePudding user response：

The way most rich text editors does it is by keeping their own internal state, updating it on key down events and rendering a custom visual layer. For example like this:

const $editor = document.querySelector('.editor');
const state = {
 cursorPosition: 0,
 contents: 'hello world'.split(''),
 isFocused: false,
};


const $cursor = document.createElement('span');
$cursor.classList.add('cursor');

const renderEditor = () => {
  const $contents = state.contents
    .map(char => {
      const $span = document.createElement('span');
      $span.innerText = char;
      return $span;
    });
  
  $contents.splice(state.cursorPosition, 0, $cursor);
  
  $editor.innerHTML = '';
  $contents.forEach(el => $editor.append(el));
}

document.addEventListener('click', (ev) => {
  if (ev.target === $editor) {
    $editor.classList.add('focus');
    state.isFocused = true;
  } else {
    $editor.classList.remove('focus');
    state.isFocused = false;
  }
});

document.addEventListener('keydown', (ev) => {
  if (!state.isFocused) return;
  
  switch(ev.key) {
    case 'ArrowRight':
      state.cursorPosition = Math.min(
        state.contents.length, 
        state.cursorPosition   1
      );
      renderEditor();
      return;
    case 'ArrowLeft':
      state.cursorPosition = Math.max(
        0, 
        state.cursorPosition - 1
      );
      renderEditor();
      return;
    case 'Backspace':
      if (state.cursorPosition === 0) return;
      delete state.contents[state.cursorPosition-1];
      state.contents = state.contents.filter(Boolean);
      state.cursorPosition = Math.max(
        0, 
        state.cursorPosition - 1
      );
      renderEditor();
      return;
    default:
      // This is very naive
      if (ev.key.length > 1) return;
      state.contents.splice(state.cursorPosition, 0, ev.key);
      state.cursorPosition  = 1;
      renderEditor();
      return;
  }  
});

renderEditor();

.editor {
  position: relative;
  min-height: 100px;
  max-height: max-content;
  width: 100%;
  border: black 1px solid;
}

.editor.focus {
  border-color: blue;
}

.editor.focus .cursor {
  border: black solid 1px;
  animation-name: blink;
  animation-duration: 1s;
  animation-iteration-count: infinite;
}

@keyframes blink {
  from {opacity: 0;}
  50% {opacity: 1;}
  to {opacity: 0;}
}

<div class="editor"></div>