TypeError: Class constructor Alg1 cannot be invoked without 'new'

[rnemec]

I have two classes: Alg1 extends Alg2.
When I rewire Alg2 and call its constructor new Alg2(),I get the error in the title.
Only fails on 3.0.0. Downgrading to 2.5.2 for now - all works fine there.

[JvJefke]

Could you give the exact error?

[rnemec]

TypeError: Class constructor Alg1 cannot be invoked without 'new'
😄

[JvJefke]

I cannot reproduce this error. Would you be willing to give some example code where you experience this error? You're node version could also help :)

[rnemec]

Node: 8.9.1
I'll try to find some time to create a reproducible example.

[rnemec]

Here is the most trivial example. Three files in the same folder.
alg1.js:

class Alg1 {}
module.exports = Alg1;

alg2.js:

const Alg1 = require('./alg1');
class Alg2 extends Alg1 {}
module.exports = Alg2;

algtest.js:

const rewire = require('rewire');
const Alg = rewire('./alg2');
let a = new Alg();

Run node algtest, resulting in:

Alg2 = function (_Alg) {_inherits(Alg2, _Alg);function Alg2() {_classCallCheck(this, Alg2);return _possibleConstructorReturn(this, (Alg2.__proto__ || Object.getPrototypeOf(Alg2)).apply(this, arguments));}return Alg2;}(Alg1);
           ^

TypeError: Class constructor Alg1 cannot be invoked without 'new'
  at new Alg2 (/Users/rnemec/Projects/T/app/util/alg2.js:2:180)
  at Object.<anonymous> (/Users/rnemec/Projects/T/app/util/algtest.js:3:9)
  at Module._compile (module.js:635:30)
  at Object.Module._extensions..js (module.js:646:10)
  at Module.load (module.js:554:32)
  at tryModuleLoad (module.js:497:12)
  at Function.Module._load (module.js:489:3)
  at Function.Module.runMain (module.js:676:10)
  at startup (bootstrap_node.js:187:16)
  at bootstrap_node.js:608:3

[rnemec]

@JvJefke - did the example help to reproduce? It's 3 files, total 8 lines of code, and it's 100% reproducible for me. Please, have a look

[JvJefke]

Thanks for the example!
I didn't have the time yet to look into this. I'll try to do it this evening.

[JvJefke]

I still can't reproduce this error. I added a test with your example, but it doesn't fail in node 8.9.1 on my computer.

see: JvJefke@35d4398

[rnemec]

Hmm, weird.

I wonder - do you babelize your tests? What happens if you just run the test (or just a code that rewire-s and instantiates, like my 3rd file) from command line using plain node?

[JvJefke]

I also ran it from command line using plain node and it still worked.

Rewire uses babel internally to convert constants (const) to variables (var), but the tests itself aren't babelized.

Could you perhaps pull the bugfix/class-constructor branch from my fork (https://github.com/JvJefke/rewire/tree/bugfix/class-constructor) and run npm test to see if it issue is environment related or not?

[rnemec]

Pulled the branch and npm test succeeds with 63 passing tests. Will play with it more to see what may be going on... One difference I see is that I'm using rewire as npm module, not running inside, like your tests.

[rnemec]

Oh, found what is causing it: I have a .babelrc in the project root that is used for some other code. When I temporarily remove the babelrc, rewire works OK. It seems that your use of babel picks up the babel setting in my project (and those settings are not rewire-friendly, apparently).

Please, let me know if there is anything I can do to help resolving this...
Oh, my .babelrc is:

{
    "presets": ["es2015"],
    "plugins": ["transform-class-properties"]
}

[JvJefke]

I opened a PR to fix this: #123.
Thanks a lot for reporting this and helping us look for a solution!

[rnemec]

My pleasure! Thanks guys for keeping this tool being one of top unit-testing utilities.