How to run bcrypt code automatically when Instantiate a class in typescript

Question

I came across some issues with async await when instantiating a class. I have a class user, and when instantiated I wish to automatically hash the password and assign it to the password.

class User {
    public userId: string;
    public password: string = '';

    constructor(public userName: string, public plainPassword: string, public email: string) {
        this.userId     = uuidv4()
        this.userName   = userName;
        this.email      = email.toLowerCase();
        this.hashPassword();
    }

    private async hashPassword(): Promise<void> {
        try {
            const salt = await bcrypt.genSalt(10);
            this.password = await bcrypt.hash(this.plainPassword, salt);
        } 
        catch (error) {
            throw error
        }
    }

The hash password returns nothing. But is a promise function, so when I do tests, I dont get any of the User keys... email, password, userId and username are undefined...

Can you help me?

Does this answer your question? async constructor functions in TypeScript? — Prerak Sola
– Prerak Sola, Commented Oct 2, 2023 at 17:15
The other alternative is to use hashSync instead of hash. Ref: github.com/kelektiv/node.bcrypt.js#to-hash-a-password-1 — Prerak Sola
– Prerak Sola, Commented Oct 2, 2023 at 17:20
@PrerakSola A terrible, terrible alternative for a backend app. — AKX
– AKX, Commented Oct 2, 2023 at 17:29
@AKX Agreed on the point that there are better options. But overall, it depends on the use case. I wouldn't discard it completely if it serves the purpose and down sides are acceptable. — Prerak Sola
– Prerak Sola, Commented Oct 2, 2023 at 17:34

rahpuser · Accepted Answer · 2023-10-02 18:58:34Z

As @akx mentioned, having async constructors in JavaScript/TypeScript is impossible. However, we can circumvent this limitation by leveraging design patterns.

Let's explore two quick alternatives:

Builder pattern

import { v4 as uuidv4 } from 'uuid';
import bcrypt from 'bcryptjs';

class User {
    public userId: string;
    public password: string = '';

    constructor(public userName: string, public plainPassword: string, public email: string) {
        this.userId = uuidv4();
        this.userName = userName;
        this.email = email.toLowerCase();
        this.plainPassword = plainPassword;
    }

    public async hashPassword(): Promise<void> {
        try {
            const salt = await bcrypt.genSalt(10);
            this.password = await bcrypt.hash(this.plainPassword, salt);
        } catch (error) {
            throw error;
        }
    }
}

class UserBuilder {
    private user?: User;

    public initialize(userName: string, plainPassword: string, email: string): UserBuilder {
        this.user = new User(userName, plainPassword, email);
        return this;
    }

    public async build(): Promise<User|null> {
        if (this.user) {
            await this.user.hashPassword();
            return this.user;
        }
        return null;
    }
}

async function clientCode() {
    const user = await new UserBuilder()
        .initialize('John Doe', 'password', '[email protected]')
        .build();
        
    console.log(user);
}

clientCode();

Factory pattern

import { v4 as uuidv4 } from 'uuid';
import bcrypt from 'bcryptjs';

class User {
    public userId: string;
    public password: string = '';

    private constructor(public userName: string, public plainPassword: string, public email: string) {
        this.userId = uuidv4();
        this.userName = userName;
        this.email = email.toLowerCase();
        this.plainPassword = plainPassword;
    }

    public async hashPassword(): Promise<void> {
        try {
            const salt = await bcrypt.genSalt(10);
            this.password = await bcrypt.hash(this.plainPassword, salt);
        } catch (error) {
            throw error;
        }
    }

    // factory method to create a User instance
    public static async createUser(userName: string, plainPassword: string, email: string): Promise<User> {
        const user = new User(userName, plainPassword, email);
        await user.hashPassword();
        return user;
    }
}

// Using the factory method
async function clientCode() {
    const user = await User.createUser('John Doe', 'password', '[email protected]');
    console.log(user);
}

clientCode();

In essence, both patterns allow you to control the instantiation process, enhancing the readability and maintainability of your code. While these patterns may not offer a direct solution to the absence of async constructors in JavaScript/TypeScript, they effectively address the underlying problem.

Thats perfect. The Factory pattern is the one most suitable for my thing... The builder pattern I seen is adding more complexity. Thank you

AKX · Accepted Answer · 2023-10-02 17:09:43Z

You're not waiting for the asynchronous function to finish, and there's no way to do so in a constructor (since a constructor can't be async).

If you really want hashing to occur asynchronously "in" the constructor, the password field would have to be a promise of a password that will get eventually fulfilled:

async function hashPassword(
  password: string,
): Promise<string> {
  const salt = await bcrypt.genSalt(10);
  return bcrypt.hash(password, salt);
}

class User {
  public userId: string;
  public passwordHashPromise: Promise<string>;

  constructor(
    public userName: string,
    public plainPassword: string,
    public email: string,
  ) {
    this.userId = uuidv4();
    this.userName = userName;
    this.email = email.toLowerCase();
    this.passwordHashPromise = hashPassword(plainPassword);
  }
}

and to access it, you'd then do

const user = new User("foo", "bar", "[email protected]");
const passHash = await user.passwordHashPromise;

Collectives™ on Stack Overflow

How to run bcrypt code automatically when Instantiate a class in typescript

2 Answers 2

Builder pattern

Factory pattern

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Builder pattern

Factory pattern

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related