如題,代碼如下:<ul class="demo">    <li>1</li>    <li>2</li>    <li>3</li>    <li>4</li>    <li>5</li>    <li>6</li></ul><script>    var l = document.getElementsByClassName("demo")[0];    var a = l.children;    var r=a.shift();    console.log(r);//報(bào)錯(cuò):a.shift is not a function?</script>類(lèi)數(shù)組對(duì)象不能調(diào)用shift方法api?