将canvas导出为图片
var canvas = document.getElementById("canvasID");canvas.toBlob(function(blob) {var a = document.createElement("a"); var body = document.getElementsByTagName("body"); document.body.
var canvas = document.getElementById("canvasID");canvas.toBlob(function(blob) {var a = document.createElement("a"); var body = document.getElementsByTagName("body"); document.body.