此回调在此代码中如何工作？

Question

I am confused how cb(); is working? What does it do?

 beforeCreate: function(user, cb) {
    bcrypt.genSalt(10, function(err, salt) {
        bcrypt.hash(user.password, salt, function(err, hash) {
            if (err) {
                console.log(err);
                cb(err);
            } else {
                user.password = hash;
                cb();
            }
        });
    });
}

Answer 1

Assuming I understand your question, what you're probably not understanding is that cb isn't defined in your sample - it's a reference to something that will be passed in as a parameter to beforeCreate .

Assuming you have your code above you would then, at some point, call beforeCreate and pass into it a method (callback) that will be used inside - like this

beforeCreate({name:"Joe"}, /* user */
  function(err){ /* callback */
    if(err) return console.log("beforeCreate callback has been called with error" + err); /* check if there is error and return from function */
    console.log("beforeCreate called successful") /* otherwise called succesfull */
  }
)

So... that anonymous function in there (after the / callback / comment is the callback that you're passing in (as a reference) to beforeCreate and what you *do with it is defined IN beforeCreate (above in your example).