Lazy

lazy.js

function lazy(promise) {
  return new Proxy(lazy, {
    get(target, prop, receiver) {
      if (prop === lazy.promise) { return promise }
      if (prop === 'catch' || prop === 'then') {
        return ((...args) => promise[prop].apply(promise, args))
      }
      return lazy(promise.then(x => x[prop]))
    },

    apply(target, thiz, args) {
      const self = thiz[lazy.promise]
      return lazy(self.then(self => promise.then(method => method.apply(self, args))))
    }
  })
}

lazy.promise = Symbol()

const fs = require('fs')

function read(file) {
  return new Promise((resolve, reject) =>
                     fs.readFile(file, (err, buf) =>
                                 err && reject(err) || resolve(buf)))
}

lazy(read('lazy.js'))
  .map(x => x + 1)
  .filter(x => x % 2)
  .toString()
  .then(text => console.log(text))
  .catch(err => console.error(err))