iframe模拟异步上传图片

<iframe id="uploadframe" width="0" height="0" style="display:none;" name="upload_target"></iframe>

<form id="uploadpic" target="upload_target" enctype="multipart/form-data" method="post" action="" style="display: none;">

<input type="file" name="uploadImg" id="uploadImg">

</form>

$(function(){

$("#uploadImg").change(function(){

   if($(this).val() && checkFile('uploadImg')){

​       $('#uploadpic').submit();

       $(this).val('');​

       return true;

       //$('#uploadpic').submit();​

   }

   return false;

});

});

function checkFile(id)

{

    extensions = 'jpg,gif,png,jpeg';

    var path = document.getElementByIdx_x_x_x_x_x_x(id).value;

    var ext = getExt(path);

    var re = new RegExp("(^|\s|,)" + ext + "($|\s|,)", "ig");

    if(extensions != '' && (re.exec(extensions) == null || ext == '')) {

        $.messager.alert("对不起，只能上传jpg, jpeg, png, gif类型的图片!");

        $('#'+id).val('');

        return false;

    }

    //showLoading();

    return true;

}

function getExt(path) {

    return path.lastIndexOf('.') == -1 ? '' : path.substr(path.lastIndexOf('.') + 1, path.length).toLowerCase();

}