Functional Programming!
Using JavaScript
and Ramda.js
by Alex Voerman
What is functional programming?
Immutability
Lamdas
Functors
Currying
Monads
Monoids
λ
Closures
Partial Application
Programming Paradigms
Imperative Programming
Object Oriented Programming
Declarative Programming
(world view)
Series of commands in steps
Keep state in Objects that talk to each other
Describe what you want to do
Functional Programming
...is Coding with Pure Functions
Pure Function
Same inputs always return same output
No side effects
Is it pure?
let cart = {
orders: [],
orderTotal: 0
};
const addToCart = order => {
cart.orders.push(order);
cart.orderTotal += order.price;
};
addToCart({ name: 'tacos', price: 2.50 });let cart = {
orders: [],
orderTotal: 0
};
const addToCart = (order, cartState) => {
cartState.orders.push(order);
cartState.orderTotal += order.price;
return cartState; // pure functions should return something
};
addToCart({ name: 'tacos', price: 2.50 }, cart);let cart = {
orders: [],
orderTotal: 0
};
const addToCart = (order, cartState) => {
// return a new object
return {
orders: cartState.push(order),
orderTotal: cartState.orderTotal + order.price
};
};
addToCart({ name: 'tacos', price: 2.50 }, cart);let cart = {
orders: [],
orderTotal: 0
};
const addToCart = (order, cartState) => {
return {
orders: [...cartState.orders, order], // <-- copies the array
orderTotal: cartState.orderTotal + order.price
};
};
addToCart({ name: 'tacos', price: 2.50 }, cart);let cart = {
orders: [],
orderTotal: 0,
startedDate: new Date(),
userId: 10 // etc
};
const addToCart = (order, cartState) => {
return {
...cartState, // <-- copies the cart object to new obj
orders: [...cartState.orders, order],
orderTotal: cartState.orderTotal + order.price
};
};
addToCart({ name: 'tacos', price: 2.50 }, cart);Arrays
Natvie JavaScript
FP Toolbox
- use const instead of let and var
- use map instead of forEach or a for-loop
- use map, filter, reduce on arrays
- use array spread [...x] to copy arrays
- use object spread {...x} or Object.assign to copy objects
Why?
Testable
Predictable
Readable
Reusable
Debuggable
Okay, but what about currying...
and higher order functions
and hardcore "real" functional programming
Ramda
More
Ramda
Functional Programming
Functional JavaScript
By Alex Voerman
