Why is this const available before the declaration?

I’m wondering why I’m able to use this const BEFORE it is declared.

The following code works fine:

import { relations } from 'drizzle-orm'
import { index, integer, pgTable, serial, uniqueIndex, varchar } from 'drizzle-orm/pg-core'

// users

export const usersTable = pgTable('users', {
    id: serial('id').primaryKey(),
    name: varchar('name'),
    email: varchar('email'),
}, (table) => ({
    nameIndex: index('users_name_index').on(table.name),
    emailIndex: uniqueIndex('users_email_index').on(table.email),
}))

export const usersRelations = relations(usersTable, ({ many }) => ({
    pets: many(petsTable),
}))

// pets

export const petsTable = pgTable('pets', {
    id: serial('id').primaryKey(),
    userId: integer('user_id'),
    name: varchar('name'),
}, (table) => ({
    nameIndex: index('pets_name_index').on(table.name),
}))

export const petsRelations = relations(petsTable, ({ one }) => ({
    user: one(usersTable, {
        fields: [petsTable.userId],
        references: [usersTable.id],
    }),
}))

As you can see, I’m referencing petsTable before it is even declared. Are exported consts available anywhere in the module? Or is this just a Drizzle thing they’ve implemented into their API?

>Solution :

Yes, this is how Javascript works. Variables are scope-bound ("hoisting"), therefore, lexically, a reference to a variable can precede its declaration:

function later() {
    console.log(FOO) // works
}

const FOO = 42

later()

However, at the runtime, you’re only allowed to use a variable after it has been actually initialized.

function later() {
    console.log(FOO) // syntactically ok, but doesn't work at runtime
}

later()

const FOO = 42