$("input[type=file]").on("change", function(){
if( /^.+\.(jpg|jpeg|png)$/.test(this.value) ){
var r = new FileReader(),
name = this.name;
r.onloadend = function(e){
$("img[for="+name+"]").attr("src", e.target.result).addClass("loadend");
};
r.readAsDataURL(this.files[0]);
}else{
this.value = "";
alert("仅支持(jpg、png)格式图片!");
}
});