JavaScript函数柯里化与组合

function add(a, b, c) {
  return a + b + c;
}

const curriedAdd = curry(add);
curriedAdd(1)(2)(3); // 6

function curry(fn) {
  return function curried(...args) {
    if (args.length >= fn.length) {
      return fn.apply(this, args);
    } else {
      return function (...nextArgs) {
        return curried.apply(this, args.concat(nextArgs));
      };
    }
  };
}

function compose(...fns) {
  return function (value) {
    return fns.reduceRight((acc, fn) => fn(acc), value);
  };
}

function pipe(...fns) {
  return function (value) {
    return fns.reduce((acc, fn) => fn(acc), value);
  };
}

const toUpper = str => str.toUpperCase();
const exclaim = str => str + '!';
const greet = str => `Hello, ${str}`;

const welcome = pipe(toUpper, exclaim, greet);
welcome('world'); // "Hello, WORLD!"

const trim = str => str.trim();
const wrap = tag => str => `<${tag}>${str}</${tag}>`;
const transform = pipe(trim, toUpper, wrap('div'));

const when = predicate => fn => value => predicate(value) ? fn(value) : value;
const logIfEven = when(x => x % 2 === 0)(x => console.log(x));