兼容IE8图片下载

图片下载：（url返回的应该是图片数据，测试发现图片链接地址如xx/xx.jpg，不能完成下载；还不适合于多个iframe的页面；跨域的图片地址不能用window.open）

downloadImg( url,filename){
		if ((navigator.userAgent.indexOf('MSIE') >= 0) && (navigator.userAgent.indexOf('Opera') < 0)) {
			var elemIF = document.createElement("iframe");
			elemIF.src = url;//文件路径
			elemIF.style.display = "none";
			document.body.appendChild(elemIF);
		}
		else {
			try {//html5中a标签有下载属性
					var $a=document.createElement('a');
					$a.setAttribute("href",url);
					$a.setAttribute("download",filename);
					var evObj = document.createEvent("MouseEvents");
					evObj.initMouseEvent('click', true, true, window, 0, 0, 0, 0, 0, false, false, true, false, 0, null);
					$a.dispatchEvent(evObj);
			} catch (e) {
			}
		}
	}

IE8;如果url是图片链接地址，并且不是跨域的图片，就是工程和图片在同一个域下,可以用这个全局对象，使用的时候直接调用downPicObj.savepic(url);

var downPicObj={
				url:null,
				objIframe:null,
				pic:null,
				count:0,
				clear:function(){
					this.url=null;
					this.objIframe=null;
					this.pic=null;
					this.count=0;
					document.all.ieimgdown=null;
				},
				savepic:function(url){					
					 if (document.all.ieimgdown == null) { 
						 downPicObj.clear();
						 downPicObj.count++;
						 if(url){
							 downPicObj.url=url;
						 }						 
						 downPicObj.objIframe = document.createElement("IFRAME"); 
						 document.body.insertBefore(downPicObj.objIframe); 
						 downPicObj.objIframe.outerHTML = "<iframe name='ieimgdown' style='display:none;' src=" + this.url + "></iframe>"; 
						 downPicObj.re = setTimeout("downPicObj.savepic()", 1) 
						 if(downPicObj.count>3){
							 downPicObj.clear();
							 clearTimeout(downPicObj.re) ;
							 
						 }
					} 
					else {						 
						downPicObj.count=0;
						clearTimeout(downPicObj.re) ;
						downPicObj.pic = window.open(this.url, "ieimgdown") 
						downPicObj.pic.document.execCommand("SaveAs") 
						document.all.ieimgdown.removeNode(true) ;
						
					} 
				}
		};

注：download

jQuery:

function download(src) {
    var $a = $("<a></a>").attr("href", src).attr("download", "img.png");
    $a[0].click();
}

原生js:

function download(src) {
    var $a = document.createElement('a');
    $a.setAttribute("href", src);
    $a.setAttribute("download", "");
    var evObj = document.createEvent('MouseEvents');
    evObj.initMouseEvent( 'click', true, true, window, 0, 0, 0, 0, 0, false, false, true, false, 0, null);
    $a.dispatchEvent(evObj);
};

如果后台返回的不是图片的具体地址，而是图片的数据流文件，返回时java端需设置header

response.setHeader("Content-disposition", "attachment; filename=" + new String("中文文件名".getBytes("utf-8"), "ISO8859-1"));  

参考链接：http://1358440610-qq-com.iteye.com/blog/2105583

https://segmentfault.com/q/1010000004988831