要进行文件的上传，需要对form表单进行特殊设置;

1.设定表单数据的提交方式为POST

2.设定enctype属性值为:multipart/form-data

<form  action="php地址"  method="post"  enctype="multipart/form-data">

   <input type="file" name="fs" id="doc">   //file必须

   <input type="submit">

</form>

//打印上传图片信息

<div id="info">   </div>

//打印图片

<img src="" id="dis">

js:

var doc = document.getElementById('doc');

var info = document.getElementById('info');

var dis = document.getElementById('dis');

doc.onchange = function(){

  var file = this.files[0];

  var html = "name:"+file.name+"<br>";

  html += "size:"+file.size+"<br>";

  html += "type:"+file.type;

  info.innerHTML = html;

//URL.createObjectURL()方法会根据传入的参数创建一个指向该参数对象的URL.

  var url = URL.createObjectURL(file);

  dis.src = url;

}