Basic FP

• Pure Function
• Curry
• Compose

Pure Function

• Given the same input, will always return the same output
• Does not have any observable side effect

Why Pure?

• Cacheable
• Portable
• Self-Documenting
• Testable

Curry

import curry from 'lodash/curry';

const match = curry(function(what, str) {
  return str.match(what);
});

match(/\s+/g, 'hello world');
// [ ' ' ]

match(/\s+/g)('hello world');
// [ ' ' ]

const hasSpaces = match(/\s+/g); // Point free

hasSpaces('hello world');
// [ ' ' ]

hasSpaces('spaceless');
// null

Compose

import { flow, map, filter, prop, toUpper } from 'lodash/fp';

const users = [
  { name: 'a', isActive: false },
  { name: 'b', isActive: true },
];

const getUpperName = flow(prop('name'), toUpper);
const getActiveUsers = filter(prop('isActive'));

flow(getActiveUsers, getUpperName)(users)
// ['A', 'B']

FP in View

• Stateless Functional Component
• Recompose

Benefits

• Pure view
• Reuse view logic
• Constraint

FP in Dataflow

• Action
• Middleware
• Reducer
• Selector

Action

• Pure object
• Use filename as action type namespace
• All handler logic in container
• API action as Promise

Middleware

• Fetch
• Global Error

Reducer

• Predefined function

Selector

• Use FP to map data
• Can be cached by reselector