Summary:
I discovered this while trying to pinpoint why Nuclide Inspector integration with RN is so flaky. It turns out that, for some reason, if I create a `WebSocket` instance early enough (which I need to when setting up DevTools integration), and the connection is fast enough (which it is on localhost), the `websocketOpen` message may arrive earlier than an `onopen` event handler is registered, causing the `onopen` handler to never fire.
```
mkdir ~/my-server
cd ~/my-server
npm i ws
nano index.js
```
Paste this code:
```js
const ws = require('ws');
const wss = new ws.Server({
port: 8099
});
```
Run the server:
```js
node index.js
```
Now, inside React Native, paste right after [these lines](57010d63b6/Libraries/Core/InitializeCore.js (L193-L194)):
```js
const ws = new window.WebSocket('ws://localhost:8099');
ws.onopen = function() {
alert('open!');
};
```
Closes https://github.com/facebook/react-native/pull/12305
Differential Revision: D4536554
Pulled By: gaearon
fbshipit-source-id: 3021fa26b3bf275cba3704a7f3a30c77db69a1f8
7a3ab96d94