Convert promise to bluebird

Use Promise.resolve - it will take any thenable, like a promise from some other implementation, and assimilate it into a Bluebird promise.

Keep in mind that the term "resolve" can be misleading, it does not mean the same as "fulfill" but can also follow another promise and settle to its result.

If you want to convert the promise to a bluebird promise resolve nothing and return the customPromise then you'll have access to all of bluebirds custom methods in the chain.

Promise.resolve().then(function(){
  return customPromise()
})

Or

Promise.resolve(customPromise())

Use Bluebird's Promise.method!

const Promise = require('bluebird');

const fn = async function() { return 'tapped!' };

bluebirdFn = Promise.method(fn);

bluebirdFn().tap(console.log) // tapped!
fn().tap(console.log) // error