Ramda

enables FP with JS

http://ramdajs.com/

What is it?

• Utility Library (comparable to Lodash, Underscore)
• pure functions, immutable state

AND:

• Every function is curried by default
• data to operate on comes last

CurrYING

apply parameters of a function in several calls

Goal: have unary functions

// A normal function with two arguments
const myFunction = (param1, param2) => { console.log(`I got called with ${param1} ${param2}` };
myFunction('Hello', 'World') // I got called with Hello World

// Now lets curry it
import {curry} from 'ramda';
const myCurriedFunction = curry(myFunction);

// does NOT execute the function, but stores the first arugment
const myCurriedHelloFunction = myCurriedFunction('Hello'); 
// ... do other things and then later
myCurriedHellFunction('World') // now prints 'I got called with Hello World');

Operated data comes last

_.forEach([1,2,3], (val) => console.log(val));
ramda.forEach((val) =>  console.log(val), [1,2,3]);

FUNCTION COMPOSITION

the big Goal

example time

https://github.com/davelosert/fp-with-ramda

Use case

The price for all selected products should be calculated and displayed as followed:

• take all price relevant products. Price relevant means: they are selected, are in stock and have type "sellable"
• sum up the the prices of all those products
• if sum is 0, return nothing, if 1, append "Dollar", else append "Dollars"