The document discusses increasing code reusability through partial application in JavaScript, particularly using ES6. It outlines various motivations and use cases for partial application, such as simplifying dependency injection and enabling lazy evaluation. The implementation of a basic partial application function and a real use case in the pagar.me library is also highlighted.

1. Increasing code
reusability through
partial application

2. Sobre
Derek Stavis
Software Engineer @ Pagar.me
github.com/derekstavis

3. Agenda
● Motivation
● Partial application
● ES6 implementation
● Use cases

4. Motivation
If you love to write generic code
function create (db, coll, doc) {
return db[coll].insert(doc)
}

5. Motivation
If you want to run away from points
const db = client.connect(...)
const createUser = (???) =>
create(db, ‘user’, ???)

6. Motivation
If you want to run away from points
const db = client.connect(...)
const createUser = (doc) =>
create(db, ‘user’, doc)

7. Motivation
If you want to run away from points
const db = client.connect(...)
const createUser = (user) =>
create(db, ‘user’, user)

8. Motivation
You will probably love partial application
const db = client.connect(...)
const createUser =
partial(create, db, ‘user’)

9. Partial application
Fill the arguments of a function
create(db, coll, doc)

10. Partial application
Fill the arguments of a function
createInDB = partial(db, create)
createInDB(coll, doc)

11. The implementation
A rudimentar version written in ES6
(f, ...left) =>
(...right) =>
f(...left, ...right)

12. Use cases

13. Dependency injection
HOF and FCF makes DI just simple
healthCheck()
.then(partial(req.status, 200))
.catch(partial(req.status, 500))

14. Lazy evaluation
Create thunks for lazy functions
const lazyHandle =
partial(handle, req, res, next)

15. You said... Promises?
Use partial application with chaining
return fetchUser(id)
.then(partial(map, getName))
.then(console.log)

16. Real use case
Pagar.me Library
https://github.com/pagarme/pagarme-js

17. Thanks