代码如下：
<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> <script> document.write(extArray.join(" ")); </script> <p> <form method=post name=upform action="/yourcgi.cgi" enctype="multipart/form-data"> <input type=file name=uploadfile size="20"> <p> <input type=button name="Submit" value="Submit" onclick="LimitAttach(this.form, this.form.uploadfile.value)"> </form>