Wrap any function in a promise to use `.then` regardless of whether that function returns a promise

promisable.js

// Simple interface used to execute a callback in different ways depending on
// whether or not a function returns a promise or not.

// Usage:
//     import Promisable from 'promisable';
//
//     Promisable(someFunction()).then(() => {
//        promiseWasSuccessful()
//     }, promiseFailed());
//
//
export default function (initialResult) {
  return new Promise((resolve, reject) => {
    // If we're dealing with a promise
    if (typeof initialResult !== 'undefined' && typeof initialResult.then === 'function') {
      initialResult.then((data) => {
        resolve(data);
      }, (error) => {
        reject(error);
      });
    // If the initialResult is just a regular variable, not a promise
    } else {
      resolve(initialResult);
    }
  });
}