错误：无法在“节点”上执行“appendChild”：新的子元素包含父

Question

下面是我的代码，它在脚本运行时抛出错误。这是添加更多菜单的代码。当我运行脚本时，它会抛出错误

  

无法在'Node'上执行'appendChild'：新的子元素包含父元素。

$(document).ready(function() {
  ulNodes = document.getElementById("sub");
  liNodes = [];
  for (var i = 0; i < ulNodes.childNodes.length; i++) {
    if (ulNodes.childNodes[i].nodeName == "LI") {
      mpData = ulNodes.childNodes[i].getAttribute('class');
      ulNodes.childNodes[i].setAttribute('class', 'n-menu' + "  " + mpData);
      liNodes.push(ulNodes.childNodes[i]);
    }
  }
  var inp = document.getElementById("sub");
  tot_Li = inp.getElementsByClassName("n-menu").length;
  var n;
  wWidth = window.innerWidth;
  if ((wWidth > 767) && (wWidth < 800)) {
    n = 4;
  }
  if ((wWidth > 800) && (wWidth < 1024)) {
    n = 5;
  }
  if (wWidth > 1025) {
    n = 7;
  }
  if (tot_Li > n) {
    myMore();
  }

  function myMore() {
    myUl = document.getElementById("sub");
    myLi = document.createElement("LI");
    myUl.appendChild(myLi);
    myLi.setAttribute('id', 'more');
    subMore = document.getElementById("more");
    subAl = document.createElement("A");
    subAl.setAttribute('href', '#nogo');
    subAl.innerHTML = "MORE";
    subMore.appendChild(subAl);
    subUl = document.createElement("UL");
    subMore.appendChild(subUl);
    subUl.setAttribute('id', 'moreUl');
    var mrUl = document.getElementById("moreUl");
    var old_Li = document.getElementsByClassName("n-menu");
    v = old_Li.length;
    nw_Li = [];
    for (var i = v; i > n; i--) //i=8    i>6
    {
      v = v - 1;
      mrUl.appendChild(old_Li[v]);
    }
  }
});