根据图片路径获取base64编码

static getUrlBase64(url, ext, callback) {
var canvas = document.createElement("canvas"); //创建canvas DOM元素
var ctx = canvas.getContext("2d");
var img = new Image;
img.crossOrigin = 'Anonymous';
img.src = url;
img.onload = function () {
canvas.height = img.height; //指定画板的高度,自定义
canvas.width = img.width; //指定画板的宽度，自定义
ctx.drawImage(img, 0, 0, img.height, img.width); //参数可自定义
var dataURL = canvas.toDataURL("image/" + ext);
callback.call(this, dataURL); //回掉函数获取Base64编码
canvas = null;
};
}