Comment utiliser DOM dans JS pour contrôler les éléments HTML

<p name="pn">hello</p>
   <p name="pn">hello</p>
   <p name="pn">hello</p>
   <script>
       function getName(){
                  var count=document.getElementsByName("pn");
                  alert(count.length);
                  var p=count[2];
                  p.innerHTML="world";
          }
   </script>

<p>hello</p>
   <p>hello</p>
   <p>hello</p>
   <script>
       function getName(){
                  var count=document.getElementsByTagName("p");
                  alert(count.length);
                  var p=count[2];
                  p.innerHTML="world";
          }
   </script>

<a id="aid" title="得到a的标签属性"></a>
   <script>
           function getAttr1(){
               var anode=document.getElementById("aid");
               var attr=anode.getAttribute("id");
               alert("a的ID是:"+attr);
            }
           function getAttr2(){
              var anode=document.getElementById("aid");
              var attr=anode.getAttribute("title");
              alert("a的title内容是："+attr);
           }
            getAttr1();
            getAttr2();
  </script>

<a id="aid2">aid2</a> 
   <script>
        function setAttr(){
           var anode=document.getElementById("aid2");
           anode.setAttribute("title","动态设置a的title属性");
           var attr=anode.getAttribute("title");
           alert("动态设置的title值为："+attr);
       }
       setAttr();
   </script>

<ul><li>1</li><li>2</li><li>3</li></ul>
   <script>
           function getChildNode(){
                var childnode=document.getElementsByTagName("ul")[0].childNodes;
                alert(childnode.length);
                alert(childnode[0].nodeType);
           }
          getChildNode();
  </script>

<p>
        <p id="pid"></p>
   </p>
   <script>
        function getParentNode(){
            var p=document.getElementById("pid");
            alert(p.parentNode.nodeName);
        }
       getParentNode();
  </script>

 <script>
       function createNode(){
             var body=document.body;
             var input=document.createElement("input");
             input.type="button";
             input.value="按钮";
             body.appendChild(input);//插入节点
        }
         createNode();
 </script>

    <script>
        function createNode(){
              var element = document.createElement("p");
              element.className = "message";
              var textNode = document.createTextNode("Hello world!");
              element.appendChild(textNode);
              document.body.appendChild(element);
        }
      createNode();
   </script>

<p id="p">
          <p id="pid">p元素</p>
    </p>
    <script>
        function addNode(){
             var p=document.getElementById("p");
             var node=document.getElementById("pid");
             var newnode=document.createElement("p");
             newnode.innerHTML="动态插入一个p元素";
             p.insertBefore(newnode,node);
        }
        addNode();
    </script>

<p id="p">
          <p id="pid">p元素</p>
    </p>
    <script>
       function removeNode(){
               var p=document.getElementById("p");
               var p=p.removeChild(p.childNodes[1]);
        }
      removeNode();
   </script>

  <script>
      function getSize(){
          var width=document.documentElement.offsetWidth||document.body.offsetWidth;//解决兼容问题
          var height=document.documentElement.offsetHeight||document.body.offsetHeight;
          alert(width+","+height);
      }
      getSize();
 </script>