<div id="div1">这是个测试</div>

 <p class="acc"></p>

 <p class="dd"></p>

  //js DOM的几个常用方法

     //document.getElementById,

     // document.getElementsByTagName,

     // document.getElementsByClassName,

     // getAttribute,

     // setAttribute

     var div1 = document.getElementById("div1").innerHTML;

     console.log(div1);//output:这是个测试

     var pars = document.getElementsByTagName("p");

     for (var i = ; i < pars.length; i++) {

         var title = pars[i].getAttribute("class");

         if (title) {

             pars[i].setAttribute("class", "look");//修改class的值为look

             console.log(pars[i].getAttribute("class"));//output:look

         }

     }

     var cls = document.getElementsByClassName("look");

     for (i in cls) {

         console.log(cls[i].innerHTML);//111,222

     }