monad.js

const RESULT = "RESULT";
const isResult = obj => obj && obj.type === RESULT;
const Result = value => ({
  type: RESULT,
  value
});

const NOTHING = "NOTHING";
const isNothing = obj => obj && obj.type === NOTHING;
const Nothing = value => ({
  type: NOTHING,
  value
});

function maybe(result) {
  if (isResult(result) || isNothing(result)) {
    return result;
  }

  if (result === undefined || result === null) {
    return Nothing(result);
  }

  return Result(result);
}

function lift(fn) {
  if (typeof fn !== "function") {
    return () => maybe(fn);
  }

  return (...args) => {
    const result = fn(...args);
    return maybe(result);
  };
}

const bind = (...fns) => init =>
  fns.reduce((prevResult, fn) => {
    if (isNothing(prevResult)) {
      return prevResult;
    }

    return fn(prevResult.value);
  }, init());

// playground
const add = val => val + 1;
const double = val => val * 2;

const monadResult = bind(lift(add), lift(double));
console.log(monadResult(lift(2)));