记录：前端将图片Url转换成base64的处理方法

 let base64String = await this.getBase64FromUrl(url);

async getBase64FromUrl(url) {
    const response = await fetch(url);
    const blob = await response.blob();
    return new Promise((resolve, reject) => {
        const reader = new FileReader();
        reader.onloadend = () => resolve(reader.result);
        reader.onerror = reject;
        reader.readAsDataURL(blob);
    });
}

方便循环处理，特地加了promise