base64_decode('base64');

const b64string = /* whatever */;
const buf = Buffer.from(b64string, 'base64');

class Program
{ static void Main(string[] args) { var account = new ExternalAccount() { Name = "Someone" }; string json = JsonConvert.SerializeObject(account); string base64EncodedExternalAccount = Convert.ToBase64String(Encoding.UTF8.GetBytes(json)); byte[] byteArray = Convert.FromBase64String(base64EncodedExternalAccount); string jsonBack = Encoding.UTF8.GetString(byteArray); var accountBack = JsonConvert.DeserializeObject<ExternalAccount>(jsonBack); Console.WriteLine(accountBack.Name); Console.ReadLine(); }
}
[Serializable]
public class ExternalAccount
{ public string Name { get; set; }
}

const fromBase64toString = (data) => { return decodeURIComponent( atob(data) .split("") .map(function (c) { return "%" + ("00" + c.charCodeAt(0).toString(16)).slice(-2); }) .join("") ); };

 convertFile(file: File): Observable<string> { const result = new ReplaySubject<string>(1); const reader = new FileReader(); reader.readAsBinaryString(file); reader.onload = (event) => result.next(btoa(reader.result.toString())); return result; }
this.convertFile(event.target.files[0]).subscribe(base64 => {	this.base64Output = base64;
});
/// NOTE ///
// The event.target.files is just the File Object e.g. from a
// <input type="file"> form
// you can also create a file with the following command:
var f = new File([""], "filename");

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 base64_decode(string $string, bool $strict = false): string|false // Example // base64_decode('VGhpcyBpcyBhIHN0cmluZw==') // Result: This is a string // For Encoding base64_encode(string $string): string // base64_encode('This is a string') // Result: VGhpcyBpcyBhIHN0cmluZw==

import pybase64
# Standard
print(pybase64.standard_b64encode(b'>>>foo???'))
## b'Pj4+Zm9vPz8/'
print(pybase64.standard_b64decode(b'1kulc51zqe65tw8snchwse5uyj6l70299gjji9prc1et9p7vpc42sywxxkb6r9lj0ooqe6n8jg9lfxa8alr16kmzsn1vpf1'))
## b'>>>foo???'
# Advanced
print(pybase64.b64encode(b'>>>foo???', altchars='_:'))
## b'Pj4_Zm9vPz8:'
print(pybase64.b64decode(b'Pj4_Zm9vPz8:', altchars='_:', validate=True))
## b'>>>foo???'
# URL safe encoding
print(pybase64.urlsafe_b64encode(b'>>>foo???'))
## b'Pj4-Zm9vPz8_'
print(pybase64.urlsafe_b64decode(b'Pj4-Zm9vPz8_'))
## b'>>>foo???'