quick-lint-js

Find bugs in JavaScript programs.

E0156: private properties are not allowed in object literals

Classes can declare private properties with #. Object cannot have private properties. It is a syntax error to declare a private property in an object literal:

class Account {
  #email;
  #password;

  async save(db) {
    await db.saveAccount({
      #email,
      #passwordHash: hashPassword(this.#password),
    });
  }
}

class DataSmuggler {
  #contraband;

  setContraband(object, contraband) {
    return {
      ...object,
      #contraband: contraband,
    };
  }

  getContraband(object) {
    return object.#contraband;
  }
}

To fix this error, rename the properties to exclude the #:

class Account {
  #email;
  #password;

  async save(db) {
    await db.saveAccount({
      email: this.#email,
      passwordHash: hashPassword(this.#password),
    });
  }
}

Alternatively, use a Symbol to attach private data to an object:

const Contraband = Symbol('contraband');
class DataSmuggler {
  setContraband(object, contraband) {
    return {
      ...object,
      [Contraband]: contraband,
    };
  }

  getContraband(object) {
    return object[Contraband];
  }
}

Documentation for other errors