Using Node.Js Modules, how do I use an object function in the same module?

Question

I have an authentication module with methods I would like to use across the server. I would like to use the rndString() method in both the module itself and export it to use in other ways throughout the app. What am I doing wrong to cause this to not work?

const crypto = require('crypto');

let sha512 = (password, salt) => {
    let hash = crypto.createHmac('sha512', salt);
    hash.update(password);
    let value = hash.digest('hex');
    return {
        salt: salt,
        passwordHash: value
    }
};

module.exports = {
    rndString: (length) => {
        return crypto.randomBytes(Math.ceil(length/2))
            .toString('hex')
            .slice(0,length);
    },
    hashId: (id) => {
        let key  = crypto.createCipher('aes-128-cbc', 'kranky');
        let hash = key.update(id, 'utf8', 'hex');
        hash += key.final('hex');
        return hash;
    },
    saltPass: (userpassword) => {
        let salt         = this.rndString(16);
        let passwordData = sha512(userpassword, salt);
        return {
            hashValue: passwordData.passwordHash,
            salt: passwordData.salt
        }
    },
    userSalt: (userpassword, salt) => {
        let passwordData = sha512(userpassword, salt);
        return passwordData.passwordHash;
    }
};

hackerrdave · Accepted Answer · 2018-09-25 00:06:57Z

You are referencing the rndString function as this.rndString inside a function that is assigned to the object key here:

saltPass: (userpassword) => {
    let salt         = this.rndString(16);
    let passwordData = sha512(userpassword, salt);

In this case, this is actually referring to the function, rather than the object in which the function is nested. You can alternatively use ES6 method syntax to get the right context:

module.exports = {
  rndString(length) {
    return crypto.randomBytes(Math.ceil(length/2))
        .toString('hex')
        .slice(0,length);
  },
  hashId(id) {
    let key  = crypto.createCipher('aes-128-cbc', 'kranky');
    let hash = key.update(id, 'utf8', 'hex');
    hash += key.final('hex');
    return hash;
  },
  saltPass(userpassword) {
    let salt         = this.rndString(16);
    let passwordData = sha512(userpassword, salt);
    return {
        hashValue: passwordData.passwordHash,
        salt: passwordData.salt
    }
  },
  userSalt(userpassword, salt) {
    let passwordData = sha512(userpassword, salt);
    return passwordData.passwordHash;
  }
}

You can find good documentation here for object method shorthand: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Method_definitions

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