Why isMatch is always false?

Question

Node.js

Why isMatch is always false? If you print candidatePassword and this.password, then they are the same.

userSchema.methods.comparePassword = function comparePassword(candidatePassword, cb) {
  bcrypt.compare(candidatePassword, this.password, (err, isMatch) => {
    cb(err, isMatch);
  });
};

Here is a function with password encryption:

userScema.pre('save', function preSave(next) {
    const user = this;
    if (!user.isModified('password')) { return next();}
        bcrypt.genSalt(10, (err, salt) => {
            if (err) {return next(err); }
            bcrypt.hash(user.password, salt, (err, hash) => {
                if (err) {return next(err);}
                user.password = hash;
                next();
            });
        });
    })

What is the problem?