“UnhandledPromiseRejectionWarning” error even when catch is present

Question

So I have this code, createExampleDir is not yet implemented, so the test fails:

let chai    = require('chai');
let expect  = chai.expect;
let homeDir = require('home-dir');
let lib     = require('../lib.js');

chai.use(require('chai-fs'));

let dir     = homeDir('/example-dir');

describe('lib', () =>
  describe('createExampleDir', () =>
    it('should find ~/example-dir', () => lib.createExampleDir()
      .then(() => expect(dir).to.be.a.directory())
      .catch(() => {throw Error('Who cares!');})
    )
  )
);

The problem is that I'm getting an UnhandledPromiseRejectionWarning error, the error "Who cares!" is throw, so the catch happens:

(node:30870) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 2): [object Object] (node:30870) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

What should I do to avoid the UnhandledPromiseRejectionWarning warning?

The catch block is entered because lib. createExampleDir is undefined. Then you throw from there. That is not handled. What you should do, is obvious from there: catch the Who cares error in an outer catch block. — marekful
Thanks @marekful, I'm still new to promises and async, I didn't understand your comment. — Nabil Kadimi
"the error "Who cares!" is thrown, so the catch happens" - no, it's exactly the other way round. Some error is happening, so the catch callback gets invoked, which then throws the "Who cares" exception that isn't handled anywhere. — Bergi

Max Sherbakov Max Sherbakov · Accepted Answer · 2018-06-12T11:09:30

add this code after chai.use

process.on('unhandledRejection', e => {
  console.error(e);
});

And you can catch error and code string number.

“UnhandledPromiseRejectionWarning” error even when catch is present

1 Answers