URL to Blob

public urlToBlob(url) {
        const self = this;
        const image = new Image();
        image.crossOrigin = '';
        image.src = url;
        image.onload = function () {
            // 图片的绝对路径地址 转换成base64编码 如下代码：
            const canvas = document.createElement('canvas');
            canvas.width = image.width;
            canvas.height = image.height;
            const ctx = canvas.getContext('2d');
            ctx.drawImage(image, 0, 0, image.width, image.height);
            // canvas.toBlob((res) => {
            //     console.log(res);
            //     self.communityFormData.delete('image');
            //     self.communityFormData.append('image', res);
            //     console.log(self.communityFormData.get('image'));
            // });
            const ext = image.src.substring(image.src.lastIndexOf('.') + 1).toLowerCase();
            const dataURL = canvas.toDataURL('image/' + ext);
            const type = 'image/' + ext;
            console.log(dataURL);
            const bytes = window.atob(dataURL.split(',')[1]); // 去掉url的头，并转换为byte
            console.log(bytes);
            // 处理异常,将ascii码小于0的转换为大于0
            const ab = new ArrayBuffer(bytes.length);
            console.log(ab);
            const ia = new Uint8Array(ab);
            console.log(ia);
            for (let i = 0; i < bytes.length; i++) {
                ia[i] = bytes.charCodeAt(i);
            }
            console.log(ia);
            const tempBlob = new Blob([ia], { type: type });
            self.communityFormData.delete('image');
            self.communityFormData.append('image', tempBlob);
            console.log(tempBlob);
        };
    }

将服务端传过来的图片绝对地址转成 Blob 类型返回给 服务端