用来获取页面背景的书签（页面背景是DataURI）

javascript : function saveAs(blob, filename) {var type = blob.type;var force_saveable_type = 'application/octet-stream';if (type && type != force_saveable_type) {var slice = blob.slice || blob.webkitSlice || blob.mozSlice;blob = slice.call(blob, 0, blob.size, force_saveable_type);}var URL = URL || webkitURL || window;var url = URL.createObjectURL(blob);var save_link = document.createElementNS('http://www.w3.org/1999/xhtml', 'a');save_link.href = url;save_link.download = filename;var event = document.createEvent('MouseEvents');event.initMouseEvent('click', true, false, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);save_link.dispatchEvent(event);URL.revokeObjectURL(url);};function dataURItoBlob(dataURI) {var byteString;if (dataURI.split(',')[0].indexOf('base64') >= 0)byteString = atob(dataURI.split(',')[1]);elsebyteString = unescape(dataURI.split(',')[1]);var mimeString = dataURI.split(',')[0].split(':')[1].split(';')[0];var ia = new Uint8Array(byteString.length);for (var i = 0; i < byteString.length; i++) {ia[i] = byteString.charCodeAt(i);}return new Blob([ia], {type : mimeString});};void(function (d) {var dataURL = d.body.style.backgroundImage;var blob = dataURItoBlob(dataURL.substr(4, dataURL.length - 5));saveAs(blob, 'image.jpeg');}(document));