_ref not defined in Create react app.

We are planning to use greenlet to defer expensive computations to web worker in CRA project ( along with Type script ). To test it out I was playing around with a small example.

**greenlet-helpers.ts**

```
import greenlet from 'greenlet';

export const greenletRead = greenlet(async msg => {
return msg;
});
```

**utils.ts**
```
import { greenletRead } from './greenlet-helpers';

try {
const resp = await greenletRead('Hey from greenlet');
console.log(resp);
} catch (e) {
console.log('Exception', e);
}
```

Running into `_ref is not defined` when ever this gets invoked. It would be great if I can get any pointers to get this started.

P.S. I also tried moving the code snippet from `greenlet-helpers` to `uitils` and still running into the same issue.

**utils.ts**
```
import greenlet from 'greenlet';

try {
const greenletRead = greenlet(async msg => {
return msg;
});

const resp = await greenletRead('Hey from greenlet');
console.log(resp);
} catch (e) {
console.log('Exception', e);
}
```