Tamper-Proof Object Encapsulation via Non-Enumerable Symbols

const SecretKey = Symbol('secretKey');
 
class SecureVault {
  constructor(secretValue) {
    Object.defineProperty(this, SecretKey, {
      value: secretValue,
      writable: false,
      enumerable: false,
      configurable: false
    });
    Object.preventExtensions(this);
  }
 
  verifySecret(candidate) {
    return Reflect.get(this, SecretKey) === candidate;
  }
}
 
const vault = new SecureVault('topSecret123');
console.log(Object.keys(vault)); // []
console.log(vault.verifySecret('topSecret123')); // true