API Server

router.param(name, callback)

• callback(req, res, next, id)
• Can be used to validate parameters on routes (ie: user data) and adding it to the req
• We can customize the function signature by in putting a function. router.param(fn(){ return fn(req, res, next, val){}})

Mongoose Middleware

• Often called pre and post hooks

• Used with async functions within the schema

• 4 types:

• 1. where this = document: validate, save, remove, init
• 2. where this = model: insertMany
• 3. where this = aggregate: aggregate
• 4. where this = query: count, deleteMany, deleteOne, find, findOne, findOneAndDelete, findOneAndRemove, findOneAndUpdate, remove, update, updateOne, updateMany

• Pre middleware operates one after another - defined by the flow of 'next'

• you can use async/await to return promises (this is a better way to control flow compared to 'next')

• Post middleware operates after the pre middleware and hooked method have completed