JS动态创建元素的两种方法

 <div id="container">
 </div>
 <script>
  window.onload = function () {
   var str='';
   for(var i=0; i<30 ;i++){
    var r = parseInt(Math.random()*100); //随机生成一个数字
    str += '<div>'+r+'</div>'; //拼接str
   }
   document.getElementById('container').innerHTML=str;
  }
 </script>

<div id="div-input">
 <input type="text" id="txt_input" value="4"/>
 <input type="button" id="leftInsert" value="左侧入" />
 <input type="button" id="rightInsert" value="右侧入" />
</div>
<div id="container">
 <span>1</span>
 <span>2</span>
 <span>3</span>
</div>
 <script>
  window.onload = function () {
   var inputValue= document.getElementById('txt_input').value;
   document.getElementById('leftInsert').onclick=function(){
    //左侧入
    var span = document.createElement('span'); //1、创建元素
    span.innerHTML=inputValue;
    var container = document.getElementById('container'); //2、找到父级元素
    container.insertBefore(span,container.childNodes[0]);//插入到最左边
   }
   document.getElementById('rightInsert').onclick=function(){
    //右侧入
    var span = document.createElement('span'); //1、创建元素
    span.innerHTML=inputValue;
    var container = document.getElementById('container'); //2、找到父级元素
    container.appendChild(span); //3、在末尾中添加元素
   }
  }
 </script>