允许使用execCommand在contentEditable div中进行Tabbing

function insertTab(div) {
  var range = window.getSelection().getRangeAt(0);
  var tabNode = document.createTextNode('\t');
  range.insertNode(tabNode);
  range.setStartAfter(tabNode);
  range.setEndAfter(tabNode);
  range.collapse(false);
}

div[contenteditable] {
  white-space: pre;
  tab-size: 4;
}

div.addEventListener('keydown', function(event) {
  if (event.key === 'Tab') {
    event.preventDefault();
    insertTab(div);
  }
});

div.addEventListener('paste', function(event) {
  var text = event.clipboardData.getData('text/plain');
  var tabRegex = /\t/g;
  var spaces = '    ';
  text = text.replace(tabRegex, spaces);
  document.execCommand('insertText', false, text);
  event.preventDefault();
});