//将图片转换成base64        function getBase64Image(url, callback){          var canvas = document.createElement(‘canvas‘),              ctx = canvas.getContext(‘2d‘),              img = new Image();          //为了解决跨域，可以直接img.crossOrigin=‘‘就能解决图片跨域问题          img.crossOrigin = ‘xes‘;          img.onload = function(){              canvas.height = img.height;              canvas.width = img.width;              ctx.drawImage(img,0,0);              var dataURL = canvas.toDataURL(‘image/png‘);              callback.call(this, dataURL);              canvas = null;           }          img.src = http://www.mamicode.com/url;>