在firefox下使用js清空file控件的value非常簡單,即:obj.value=""; 就可以了,但在ie下,由於出於安全等方面考慮,file的value被設爲了只讀,所以js對其不能直接地控制,因此我們只能使用一些變通的方法來解決,網上對此也有好些方法,在此我談談自己認爲最好的幾種。
下面以上傳文件格式限制(只對擴展名判斷)這一實例來說明。
1、file控件由HTML生成
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script>
function CheckUpLoadFile(obj) {
DenyExt = "exe|cmd|jsp|php|asp|aspx|html|htm";
var FileExt = "";
FileExt = obj.value.substr(obj.value.lastIndexOf(".") + 1).toLowerCase();
if (DenyExt.indexOf(FileExt) != -1) {
alert("You can't upload the file of the types:" + DenyExt);
if (!window.addEventListener) {
//IE 關鍵代碼在這裏!!!
//方法一(此方法最佳!):
obj.outerHTML+='';
//方法二:
// var newObj= obj.cloneNode(true);
// newObj.value=''; // 設置新控件value爲空
// obj.parentNode.replaceChild(newObj, obj);
} else {
//非IE
obj.value = "";
return false;
}
}
}
</script>
<title>無標題文檔</title>
</head>
<body>
<span id="attachments_span">
<input type="file" name="myfile" οnchange="CheckUpLoadFile(this);">
</span>
</body>
</html>
2、file控件由JS動態生成
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script>
function addUploadField(name, parentId) {
var f = document.createElement("input");
f.type = "file";
f.name = name;
if (window.addEventListener) { // Mozilla, Netscape, Firefox
f.addEventListener("change", function() {
CheckUpLoadFile(f, parentId);
}, false);
} else { // IE
f.attachEvent('onchange', function() {
CheckUpLoadFile(f, parentId);
});
}
f.size = 30;
p = document.getElementById(parentId);
p.appendChild(document.createElement("br"));
p.appendChild(f);
}
function CheckUpLoadFile(obj) {
DenyExt = "exe|cmd|jsp|php|asp|aspx|html|htm";
if (obj.value == "") {
return false;
}
var FileExt = "";
FileExt = obj.value.substr(obj.value.lastIndexOf(".") + 1).toLowerCase();
if (DenyExt.indexOf(FileExt) != -1) {
alert("You can't upload the file of the types:" + DenyExt);
if (!window.addEventListener) {
//IE 關鍵代碼在這裏!!!
obj.select();
document.execCommand('Delete');
obj.blur();
//obj.outerHTML+=''; 此方法雖然很安全,但可惜在此不能使用
return false;
} else {
//非IE
obj.value = "";
return false;
}
}
}
</script>
<title>無標題文檔</title>
</head>
<body>
<span id="attachments_span">
<input type="button" name="add" οnclick="addUploadField('myFile' ,'attachments_span');" value="Add" />
</span>
</body>
</html>