html2canvas(document.getElementById("id1"), { 
onrendered: function(canvas) { 
document.getElementById("id2").appendChild(canvas);//生成画布后如何处理，当然可以在新标签打开，在浮层展示等等 
}, 
canvas_id: 'canvas'//通过修改html2canvas源码添加canvas的id 
});

var canvas = document.getElementById("<span style="font-family: Arial, Helvetica, sans-serif;">canvas"</span><span style="font-family: Arial, Helvetica, sans-serif;">),</span> 
url = canvas.toDataURL();// 
//以下代码为下载此图片功能 
var triggerDownload = $("<a>").attr("href", url).attr("download", "img.png").appendTo("body"); 
triggerDownload[0].click(); 
triggerDownload.remove();