Comment insérer du texte à la position du curseur dans une zone de texte à l'aide de JavaScript ?

function insertAtCaret(areaId, text) {
  // Get the textarea element
  var txtarea = document.getElementById(areaId);

  // Check if the element exists
  if (!txtarea) {
    return;
  }

  // Determine the browser type (Internet Explorer or others)
  var br = ((txtarea.selectionStart || txtarea.selectionStart == '0') ?
    "ff" : (document.selection ? "ie" : false));

  // Calculate the cursor position
  var strPos = 0;
  if (br == "ie") {
    txtarea.focus();
    var range = document.selection.createRange();
    range.moveStart('character', -txtarea.value.length);
    strPos = range.text.length;
  } else if (br == "ff") {
    strPos = txtarea.selectionStart;
  }

  // Create a string that consists of the text before, after, and the inserted text
  var front = (txtarea.value).substring(0, strPos);
  var back = (txtarea.value).substring(strPos, txtarea.value.length);
  txtarea.value = front + text + back;

  // Reset the cursor position after inserting the text
  strPos = strPos + text.length;
  if (br == "ie") {
    txtarea.focus();
    var ieRange = document.selection.createRange();
    ieRange.moveStart('character', -txtarea.value.length);
    ieRange.moveStart('character', strPos);
    ieRange.moveEnd('character', 0);
    ieRange.select();
  } else if (br == "ff") {
    txtarea.selectionStart = strPos;
    txtarea.selectionEnd = strPos;
    txtarea.focus();
  }
}

<textarea>