How to use the JavaScript bcrypt library

Find out how to hash and check passwords in JavaScript with the bcrypt library

⭐️ 👀 2023 WEB DEVELOPMENT BOOTCAMP starting in days! Join the waiting list to reserve your spot in my 10-weeks cohort course and learn the fundamentals, HTML, CSS, JS, Tailwind, React, Next.js and much much more! 👀 ⭐️

The bcrypt npm package is one of the most used packages to work with passwords in JavaScript.

This is security 101, but it’s worth mentioning for new developers: you never store a password in plain text in the database or in any other place. You just don’t.

What you do instead is, you generate a hash from the password, and you store that.

In this way:

import bcrypt from 'bcrypt'
// or
// const bcrypt = require('bcrypt')

const password = 'oe3im3io2r3o2'
const rounds = 10

bcrypt.hash(password, rounds, (err, hash) => {
  if (err) {

You pass a number as second argument and the bigger that is, the more secure the hash is. But also the longer it takes to generate it.

The library README tells us that on a 2GHz core we can generate:

rounds=8 : ~40 hashes/sec
rounds=9 : ~20 hashes/sec
rounds=10: ~10 hashes/sec
rounds=11: ~5  hashes/sec
rounds=12: 2-3 hashes/sec
rounds=13: ~1 sec/hash
rounds=14: ~1.5 sec/hash
rounds=15: ~3 sec/hash
rounds=25: ~1 hour/hash
rounds=31: 2-3 days/hash

If you run bcrypt.hash() multiple times, the result will keep changing. This is key because there is no way to reconstruct the original password from a hash.

Given the same password and a hash it’s possible to find out if the hash was built from that password, using the function:, hash, (err, res) => {
  if (err) {
  console.log(res) //true or false

If so, the password matches the hash and for example we can let a user log in successfully.

You can use the bcrypt library with its promise-based API too, instead of callbacks:

const hashPassword = async () => {
  const hash = await bcrypt.hash(password, rounds)
  console.log(await, hash))


Check a couple examples in this Glitch:

One more thing! ⚠️ ✋

At the end of January I will organize the Web Development Bootcamp.

It's a 10-weeks long cohort online course where I will guide you to becoming a Web Developer.

It's not "just a course". It's a big event I organize once a year.

We'll start from zero, learn the fundamentals of Web Development, HTML CSS, JavaScript, Tailwind, Git, using the command line, VS Code, GitHub, Node.js, we'll then learn React, JSX, how to use PostgreSQL, Astro, Next.js, Prisma, deploying on Netlify/DigitalOcean/Fly/Vercel and much more! 

At the end of the first 10 weeks you'll know how to create web sites and web applications and I'll unlock you the 2nd phase of the Bootcamp: you will get access to a large number of projects exclusive to the Bootcamp graduates, so you can follow my instructions to build things like private areas with authentication, clones of popular sites like Twitter YouTube Reddit, create e-commerce sites, and much much more.

Because once you got the fundamentals, you only learn by working on real, exciting projects.

To find out more, visit