要完成此效果需要两个步骤
第一步:把如下代码加入到<head>区域中
<SCRIPT LANGUAGE="JavaScript">
<!-- Begin
extArray = new Array(".gif", ".jpg", ".png");
function LimitAttach(form, file) {
allowSubmit = false;
if (!file) return;
while (file.indexOf("//") != -1)
file = file.slice(file.indexOf("//") + 1);
ext = file.slice(file.indexOf(".")).toLowerCase();
for (var i = 0; i < extArray.length; i++) {
if (extArray[i] == ext) { allowSubmit = true; break; }
}
if (allowSubmit) form.submit();
else
alert("对不起,只能上传以下格式的文件: "
+ (extArray.join(" ")) + "/n请重新选择符合条件的文件"
+ "再上传.");
}
// End -->
</script>
第二步:把如下代码加入到<body>区域中
<script>
document.write(extArray.join(" "));
</script>
<p>
<form method=post name=upform action="http://www.ydaima.com/seach.asp?k=1" enctype="multipart/form-data">
<input type=file name=uploadfile>
<p>
<input type=button name="Submit" value="Submit" οnclick="LimitAttach(this.form, this.form.uploadfile.value)">
</form>