function urlToBase64(url, callback) {
    var xhr = new XMLHttpRequest();
    xhr.onload = function() {
        var reader = new FileReader();
        reader.onloadend = function() {
            callback(reader.result);
        }
        reader.readAsDataURL(xhr.response);
    };
    xhr.open('GET', url);
    xhr.responseType = 'blob';
    xhr.send();
}
var imageUrl = 'https://static.flomoapp.com/file/2023-04-02/19208/1680445554566B00B7ACEC5BE07B8.jpg?OSSAccessKeyId=LTAI4G9PcaGksWVKCPrE1TVL&Expires=1680763399&Signature=Fwxz3MC%2FfECIuyddsuQzC81MmRs%3D';

urlToBase64(imageUrl, function(base64) {
    console.log(base64); // 输出转换后的 Base64 编码
});