js如何下载图片到本地

$(function(){  
    //二维码  
    (function(){  
        var img_src = $('.qr_img')[0].src;  
        if(browserIsIe()){//假如是ie浏览器  
            $('.down_qr').on('click',function(){  
                img_src = $('.qr_img')[0].src;  
                DownLoadReportIMG(img_src);  
            });  
        }else{  
            $('.down_qr').attr('download',img_src);  
            $('.down_qr').attr('href',img_src);  
  
            $('.sutmit_btn').on('click',function(){  
                $('.down_qr').attr('download',img_src);  
                $('.down_qr').attr('href',img_src);  
            });  
        }  
          
    })();  
});  
  
function DownLoadReportIMG(imgPathURL) {  
    //如果隐藏IFRAME不存在，则添加  
    if (!document.getElementById("IframeReportImg"))  
        $('<iframe style="display:none;" id="IframeReportImg" name="IframeReportImg" onload="DoSaveAsIMG();" width="0" height="0" src="about:blank"></iframe>').appendTo("body");  
    if (document.all.IframeReportImg.src != imgPathURL) {  
        //加载图片  
        document.all.IframeReportImg.src = imgPathURL;  
    }  
    else {  
        //图片直接另存为  
        DoSaveAsIMG();  
    }  
}  
function DoSaveAsIMG() {  
    if (document.all.IframeReportImg.src != "about:blank")  
        window.frames["IframeReportImg"].document.execCommand("SaveAs");  
}  
//判断是否为ie浏览器  
function browserIsIe() {  
    if (!!window.ActiveXObject || "ActiveXObject" in window)  
        return true;  
    else  
        return false;  
}