function zll_up(click_id,up_url,text_id,show_id){

    this.create = function(){}

    //当点击指定元素时,创建iframe form input(file)等元素

    $("#"+click_id).click(function(){

        console.log('click');

        $("body").append("<form action='"+up_url+"' method='post' enctype='multipart/form-data' target='iframe_"+click_id+"' style='display:none;' name='form_"+click_id+"' id='form_"+click_id+"'><input type='file' name='tupian_"+click_id+"' id='tupian_"+click_id+"'></form>");

        $("body").append("<iframe style='display:none;' name='iframe_"+click_id+"' id='iframe_"+click_id+"'></iframe>");

        $('#tupian_'+click_id).change(function(){

            console.log('change');

            var file = document.getElementById("tupian_"+click_id).files[0];

            var reader = new FileReader();

            reader.readAsDataURL(file);

             reader.onload = function(evt){

             $("#"+show_id).html('<img style="width:100%;height:100%;" src="' + evt.target.result + '" />');

            }

            $("#form_"+click_id).submit();

        });

        $("#iframe_"+click_id).on("load",function(){

            console.log('load');

            var data = $(window.frames['iframe_'+click_id].document.body).find("textarea").html();

            console.log(data);

            $("#"+text_id).val(data);

            //当上传完成时删除之前创建的元素

            console.log('remove');

            $("#iframe_"+click_id).remove();

            $("#form_"+click_id).remove();

        });

        $("#tupian_"+click_id).click();

    });

}

<div class="control-group">

                        <label class="control-label item-label" >上传图片 (750*1525)<span class="check-tips"></span></label>

                        <div class="controls uploadrow2" data-max="1" title="点击修改图片" rel="cover" id="upclick">

                            <input type="hidden" name="img" id="img" value="{$art.img}">

                            <div class="upload-img-box" rel="img" id="imgshow" style="height:auto;">

                                <if condition="!empty($art['img'])">

                                    <img src="__UPLOADS__/{$art.img}"/>

                                </if>

                            </div>

                        </div>

                    </div>
<script type="text/javascript" src="引入上面的js代码"></script>
<script type="text/javascript">
       zll_up("upclick","{:U("$con_name/z_upload")}","img","imgshow");
</script>

function z_upload(){

        //单文件上传

        //公用上传函数 zll 2017-6-7 11:35:44

        //用于iframe的无刷新上传

        $config = array(

                'maxSize'    =>    3145728,

                'rootPath'   =>    './Uploads/',

                'savePath'   =>    '',

                'saveName'   =>    array('uniqid',''),

                'exts'       =>    array('jpg', 'gif', 'png', 'jpeg'),

                'autoSub'    =>    true,

                'subName'    =>    array('date','Ymd'),

            );

            $upload = new \Think\Upload($config);// 实例化上传类

            $info = $upload->upload();

            if(!$info) {

                // 上传错误提示错误信息

                //    echo $upload->getError();

                echo "<textarea>error</textarea>";

            }else{// 上传成功

                echo "<textarea>".$info[array_keys($info)[0]]['savepath'].$info[array_keys($info)[0]]['savename']."</textarea>";

            }

    }