Using bcrypt with promises to hash a password and then verify it

bcrypt-promise.js

const bcrypt = require("bcrypt");
// use this library in case your version of node doesn't support Promise
// const Promise = require("promise");

let password = "hello";
let stored_hash = "";

// first generate a random salt
function genSalt(password) {
  return new Promise((resolve, reject) => {
    bcrypt.genSalt(10, function(err, salt) {
      if (err) {
        reject(err);
      } else {
        resolve({
          salt: salt,
          password: password
        });
      }
    });
  });
}

// hash the password with the salt
function genHash(salt, password) {
  return new Promise((resolve, reject) => {
    bcrypt.hash(password, salt, function(err, hash) {
      if (err) {
        reject(err);
      } else {
        resolve({
          salt: salt,
          password: password,
          hash: hash
        });
      }
    });
  });
}

// execute in sequence
console.log("store");
genSalt(password)
  .then(function(result) {
    return genHash(result.salt, result.password);
  })
  .then(function(result) {
    console.log("store hash in user profile :", result);
    stored_hash = result.hash;
  })
  .catch(function(err) {
    console.log(err);
  });

// =====================================================
function lookupUser(user, passwd) {
  return new Promise((resolve, reject) => {
    // lookup the user in the stored database
    // in this case its not async so just resolve with the stored hash
    resolve({
      user: user,
      password: passwd,
      hash1: stored_hash
    });
  });
}

function reHash(user, password, hash1) {
    // extract salt from existing has (30 characters)
  let salt = hash1.substr(0, 30);
  return new Promise((resolve, reject) => {
    bcrypt.hash(password, salt,  function(err, hash2) {
      if (err) {
        reject({
            err,
            user: user,
            salt: salt,
            password: password,
            hash1: hash1, // stored hash
            hash2: hash2 // generated hash
          });
      } else {
        resolve({
          user: user,
          salt: salt,
          password: password,
          hash1: hash1, // stored hash
          hash2: hash2 // generated hash
        });
      }
    });
  });
}

// lookup and verify
setTimeout(function() {
  console.log("verify");
  lookupUser("joe", password)
    .then(function(result) {
      return reHash(result.user, result.password, result.hash1);
    })
    .then(function(result) {
      console.log(result.hash1);
      console.log(result.hash2);
      if (result.hash1 === result.hash2) {
        console.log("verified");
      } else {
        console.log("failed");
      }
    })
    .catch(function(err) {
      console.log(err);
    });
}, 1000);

I love this man.

Thanks for this ... Helped a ton

glad i could help. I worked this up after I failed horribly on an interview question about bcrypt.