serialPromise.js

// Turn any function calls on a promise into function calls on the result.
//
// For example:
//
//     serialPromise(promise).foo();
//
// Is the same as calling:
//
//     promise.then(result => result.foo());
//
function serialPromise(promise) {
  return new Proxy(promise, {
    get: (target, prop, receiver) => {
      return function() {
        return serialPromise(target.then(result => result[prop].apply(this, arguments)));
      }
    }
  })
}

test.js

// Define test structure, where promises return objects that return promises
let chain = Promise.resolve({
  foo: () => Promise.resolve({
    bar: () => Promise.resolve({
      baz: (x) => { console.log('baz', x)}
    })
  })
})

// Chaining promises manually
chain.then(x => x.foo()).then(foo => foo.bar()).then(bar => bar.baz(1))

// Serializing promises
serialPromise(chain).foo().bar().baz(2);