将input file的选择的文件清空的两种解决方案

<input type="file" id="fileupload" name="file" /> 

<!-- 1 -->
var obj = document.getElementById('fileupload') ; 
obj.select(); 
document.selection.clear(); 

<!-- 2 -->
var obj = document.getElementById('fileupload') ; 
obj.outerHTML=obj.outerHTML; 


<!-- 3 -->
var file = document.getElementById('fileupload');
file.value = '';

<!-- 4 -->
var file = document.getElementById('fileupload');
file.outerHTML = file.outerHTML; //重置了file的outerHTML