3e0a7f808c
Added precondition checks to validate input files and paths to return more informative error messages as per #2
p-is-promise 
Check if something is a promise
Why not is-promise? That module checks for a thenable, not an ES2015 promise. This one is stricter.
You most likely don't need this. Just pass your value to Promise.resolve() and let it handle it.
Can be useful if you need to create a fast path for a synchronous operation.
Install
$ npm install p-is-promise
Usage
const pIsPromise = require('p-is-promise');
const Bluebird = require('bluebird');
pIsPromise(Promise.resolve('🦄'));
//=> true
pIsPromise(Bluebird.resolve('🦄'));
//=> true
pIsPromise('🦄');
//=> false
Related
License
MIT © Sindre Sorhus