Understanding hooks in Sequelize (Returning vs. Attaching) - express

Question

I am following my school's workshop regarding how to integrate Sequelize with Express. There is a section where we are learning to leverage hooks in our models—and in it I was confused by this:
Returning vs. Attaching
A hook runs with the instance of a Page being
saved given as an argument. We want to, therefore, attach a created
urlTitle to this page instance instead of returning it from the
function.
var Sequelize = require('sequelize');
var db = new Sequelize('postgres://localhost:5432/__wikistack__', {
logging: false,
});
const Page = db.define(
'page',
{
title: {
type: Sequelize.STRING,
},
urlTitle: {
type: Sequelize.STRING,
},
content: {
type: Sequelize.TEXT,
},
status: {
type: Sequelize.ENUM('open', 'closed'),
},
},
{
hooks: {
beforeValidate: function(page) {
if (page.title) {
// Removes all non-alphanumeric characters from title
// And make whitespace underscore
return (page.urlTitle = page.title.replace(/\s/g, '_').replace(/\W/g, ''));
} else {
// Generates random 5 letter string
return (urlTitle = Math.random()
.toString(36)
.substring(2, 7));
}
},
},
}
);
Can someone explain this? How can the function in the hook not return something? The above works, so the hook/function is returning something.
Thanks in advance!

Answer 1

Hooks are just code that gets run at certain life cycle points of a record instance. You can have them be purely side effects. In your case, all you need to do is modify the page object that the hook is passed, return doesn't help or hurt.
However, the return value of a hook is not useless. If you need to do anything async inside a hook, you have to return a promise.