怎么样用js可以调起浏览器把网页上的图片下载下来？

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);
};

测试：

download("https://ss0.bdstatic.com/5aV1bjqh_Q23odCf/static/superman/img/logo/logo_whit