No listeners for <event> in DOMContentLoaded

### Expected behavior
Expecting listeners to bet ready when DOMContentLoaded is fired.

### Actual behavior
Getting warning "No listeners for myevent"

### Steps to reproduce behavior
index.js
```
app.use(require('./stores/app'))
app.use(require('./stores/user'))
```
app.js
```
emitter.on('DOMContentLoaded', function () {
// Do app-level stuff
emitter.emit('user:myevent', {})
```
user.js
```
emitter.on(`user:myevent`, function (data) {...})
```

Have to wait a bit before the listener is registered.
setTimeout(() => {emitter.emit('user:myevent', {})}, 10)

Start by reproducing the warning with the index.js, app.js, and user.js examples from the issue, then trace when each listener is registered relative to DOMContentLoaded. Done means the user:myevent listener is ready when the event fires and the warning no longer appears without using setTimeout.

Written by the indexing model from the issue text.