How do you securely register a new user with bcrypt?

Hash the submitted password with bcrypt.hash() and store only the resulting hash.

// Step 1: Hash the password
const hashedPassword = await bcrypt.hash(req.body.password, 10);

// Step 2: Store in database
db.collection('users').insertOne({
  login: req.body.username,
  hash: hashedPassword
});

// Step 3: Check for duplicate username (insertOne error)

The second parameter (10) is the cost factor - higher is more secure but slower.