JavaScript如何获得input元素value的值

在JavaScript中获取input元素value的值：

方法一：

 <!DOCTYPE html>
 <html>
 <head>
     <meta charset="utf-8">
     <meta http-equiv="X-UA-Compatible" content="IE=edge">
     <title>JavaScript中获取input元素value值</title>
     <link rel="stylesheet" href="">
     <script>
         function printInputValue() {
             var inputValue = document.getElementById("demo1").value;
             console.log(inputValue);
             document.getElementById("demo2").innerHTML = inputValue;
         }
     </script>
 </head>
 <body>
     <input type="text" id="demo1">
     <button onclick="printInputValue()">获取input元素value值</button>
     <p id="demo2"></p>
 </body>
 </html>

方法二：

 <!DOCTYPE html>
 <html>
 <head>
     <meta charset="utf-8">
     <meta http-equiv="X-UA-Compatible" content="IE=edge">
     <title>JavaScript34</title>
     <link rel="stylesheet" href="">
     <script>
         function print(){
             var a = myform.name.value;
             alert(a);
             document.getElementsByName("span")[0].innerHTML = a;
         }
     </script>
 </head>
 <body>
     <form name="myform">
         <input type="text" name="name" id="nn">
         <input type="button" name="button" value="测试" onclick="print()">
         <span name="span"></span>
     </form>
 </body>
 </html>