客户端限制只能上传jpg格式图片的js代码

function checkPhoto(fnUpload) 
{ 
var filename = fnUpload.value; 
alert(filename); 
var mime = filename.toLowerCase().substr(filename.lastIndexOf(".")); 
if(mime!=".jpg") 
{ 
alert("请选择jpg格式的照片上传"); 
fnUpload.outerHTML=fnUpload.outerHTML; 
} 
}