JS 实现图片直接下载

< a   href = "picName.jpg"     id = pic1   onclick = "savepic();return false;" style = "cursor:hand" >点击下载</ a >   

<script type="text/javascript">

function savepic() {
            if (document.all.a1 == null) {
                objIframe = document.createElement("IFRAME");
                document.body.insertBefore(objIframe);
                objIframe.outerHTML = "<iframe name=a1 style='width:400px;hieght:300px' src=" + imageName.href + "></iframe>";
                re = setTimeout("savepic()", 1)
            }
            else {
                clearTimeout(re)
                pic = window.open(imageName.href, "a1")
                pic.document.execCommand("SaveAs")
                document.all.a1.removeNode(true)
            }
        } 

</script>