原生js实现点击下载图片

<div class="form-group"> ?????<div> ??????????<h3>申请人信息</h3> ??????????<div class="sq_info"> ????????????????<ul> ?????????????????????<li><span>姓名：</span><p>张三</p></li> ?????????????????????<li><span>姓名：</span><p>张三</p></li> ?????????????????????<li><span>本人照片：</span><img src="http://pic.pptbz.com/201506/2015070581208537.JPG" alt=""><a href="javascript:void(0);" onclick="down_img(this)">点击下载</a></li> ?????????????????????<li><span>护照首页：</span><img src="https://ss2.bdstatic.com/70cFvnSh_Q1YnxGkpoWK1HF6hhy/it/u=302701032,2300144492&fm=27&gp=0.jpg" alt=""><a href="javascript:void(0);" onclick="down_img(this)">点击下载</a></li> ??????????????????????<li><span>价格：</span><p class="price">500元</p></li> ???????????????????</ul> ??????????????</div> ?????????</div> ????<div>

<script>function myBrowser() {var userAgent = navigator.userAgent; //取得浏览器的userAgent字符串var isOpera = userAgent.indexOf("Opera") > -1;if(isOpera) {return "Opera"}; //判断是否Opera浏览器if(userAgent.indexOf("Firefox") > -1) {return "FF";} //判断是否Firefox浏览器if(userAgent.indexOf("Chrome") > -1) {return "Chrome";}if(userAgent.indexOf("Safari") > -1) {return "Safari";} //判断是否Safari浏览器if(userAgent.indexOf("compatible") > -1 && userAgent.indexOf("MSIE") > -1 && !isOpera) {return "IE";}; //判断是否IE浏览器if(userAgent.indexOf("Trident") > -1) {return "Edge";} //判断是否Edge浏览器}//②IE浏览器图片保存（IE其实用的就是window.open)function SaveAs5(imgURL) {var oPop = window.open(imgURL, "", "width=1, height=1, top=5000, left=5000");for(; oPop.document.readyState != "complete";) {if(oPop.document.readyState == "complete") break;}oPop.document.execCommand("SaveAs");oPop.close();}//④点击事件下载（只需更改图片路径即可）function down_img(a){var osb = a;var sb = a.previousSibling.src;// console.log(sb)if(myBrowser() === "IE" || myBrowser() === "Edge") {//IE （浏览器）SaveAs5(sb);} else {//!IE (非IE)osb.href = sb;osb.download = "";}}</script>