chain-promise.js

const chain = (...fns) =>
  initialValue => fns.reduce(
    (result, fn) => {
      if (result && (typeof result === 'object')) {
        const then = result.then;
        if (typeof then === 'function') {
          return then.call(result, fn);
        }
      }
      return fn(result);
    },
    initialValue
  );
  
  chain(
    x => Promise.resolve(x + 1),
    x => x / 2,
    x => Promise.resolve(x / 2)
  )(0)
  .should.eventually.equal(0.25);
  
  // run it: https://jsfiddle.net/jgj4eh68/1/