Functional JS

functional.js

// Partial application
const sum = (a, b, c) => a + b + c;

const papply = (fn, ...rest) => (...last) => fn.apply(null, [...rest, ...last]);

const a = papply(sum, 5);
console.log(a(2, 3));

// currying
const curry = (fn, ...rest) => {
  const ln = fn.length;
  const fnArgs = [...rest];
  const accumulator = () => {
    if ((ln - fnArgs.length) <= 0) {
      return fn.apply(null, fnArgs);
    }
    return (x) => {
      if (x) {
        fnArgs.push(x); 
      }
      return accumulator();
    }
  }
  return accumulator();
}

const sum = (a, b, c) => a + b + c;

const add5 = curry(sum, 2, 3);

console.log(add5()(10));