JS将base64图片转换成透明底图片

/**
* dataimg      base64编码图片
* callback      回调函数
* /
changeImage: function (dataImg, callback) {
                let self = this;
                var base64Img = document.createElement("base64Img"),
                    canvas = document.createElement("canvas"),
                    context = canvas.getContext("2d");
                // 创建新图片
                var img = new Image();
                img.src = dataImg;
                img.addEventListener(
                    "load",
                    function () {
                        // 绘制图片到canvas上
                        canvas.width = img.width;
                        canvas.height = img.height;
                        context.drawImage(img, 0, 0);

                        // 将canvas的透明背景设置成白色
                        var imageData = context.getImageData(
                            0,
                            0,
                            canvas.width,
                            canvas.height
                        );
                        for (var i = 0; i < imageData.data.length; i += 4) {
                            //rgb大于250的透明度y均设置成0
                            if (
                                imageData.data[i] > 250 &&
                                imageData.data[i + 1] > 250 &&
                                imageData.data[i + 2] > 250
                            ) {
                                imageData.data[i + 3] = 0;
                            }
                        }
                        context.putImageData(imageData, 0, 0);
                        self.baseImg = canvas.toDataURL("image/png");//返回base64
                        if (typeof callback !== undefined) {
                            if (callback) callback(self.baseImg);
                        }
                    },
                    false
                );
            }