Base64 エンコード完全技術ガイド

// Standard Base64 in Node.js
const rawText = "Curious-Techie Developer Platform";
const base64Standard = Buffer.from(rawText, "utf-8").toString("base64");
console.log("Standard:", base64Standard);

// Base64URL encoding (RFC 4648 Section 5)
const base64Url = Buffer.from(rawText, "utf-8")
  .toString("base64url"); // Native modern Node support
console.log("Base64URL:", base64Url);

// Browser Web API (Uint8Array & btoa fallback)
function uint8ArrayToBase64(bytes: Uint8Array): string {
  let binary = "";
  for (let i = 0; i < bytes.byteLength; i++) {
    binary += String.fromCharCode(bytes[i]);
  }
  return btoa(binary);
}

// Safely handle unicode strings with native browser TextDecoder
function safeBase64Decode(base64Str) {
  // Normalize Base64URL back to standard Base64
  let base64 = base64Str.replace(/-/g, '+').replace(/_/g, '/');
  while (base64.length % 4) {
    base64 += '=';
  }
  const binaryString = atob(base64);
  const bytes = new Uint8Array(binaryString.length);
  for (let i = 0; i < binaryString.length; i++) {
    bytes[i] = binaryString.charCodeAt(i);
  }
  return new TextDecoder().decode(bytes);
}

const decoded = safeBase64Decode("Q3VyaW91cy1UZWNoaWU=");
console.log(decoded); // "Curious-Techie"