Strange behavior with module.exports and async in React - node.js

Question

Here's a very strange issue that has me puzzled. After creating a React app with create-react-app, I added these two files:
TestMod.js
const TestMod = {
doSomething() {
}
};
module.exports = TestMod;
Test.js
import React, { Component } from 'react';
import TestMod from './TestMod';
export default class Test extends Component {
render() {
TestMod.doSomething();
return <div>Testing</div>;
}
}
I included the Test component inside App, run npm start, and everything worked fine. Then I changed doSomething to be async, like this
TestMod.js
const TestMod = {
async doSomething() {
}
};
module.exports = TestMod;
Now I get a compilation error:
[1] ./src/Test.js
[1] 26:6-13 "export 'default' (imported as 'TestMod') was not found in './TestMod'
Why? I know how to make it work again:
TestMod.js
export const TestMod = {
async doSomething() {
}
};
Test.js
import React, { Component } from 'react';
import {TestMod} from './TestMod';
export default class Test extends Component {
render() {
TestMod.doSomething();
return <div>Testing</div>;
}
}
But what I'd like to understand is why making a function async causes module.exports to break on the React side. (By the way, it still works fine on the Node.js side).
Thanks,
Alvaro