After discussion, I added falling back to fetch based pinging when the WebSocket fails to connect. I also added an example of how to proxy the onDemandEntries WebSocket when using a custom server. Fixes: #6296
Closes: #6244
This will block the following keys:
```
NODE_.+
__.+
```
There doesn't seem to be a way to simulate a failed build or else I'd add tests for it.
Fixes#4495
Here's my approach for replacing the XHR on-demand-entries pinger #1364#4495. I'm not sure if this is the way everyone wants to accomplish this since I saw mention of using a separate server and port for the dynamic entries websocket, but thought this would be a fairly clean solution since it doesn't need that.
With this method the only change when using a custom server is you have to listen for the upgrade event and pass it to next.getRequestHandler(). Example:
```
const server = app.listen(port)
const handleRequest = next.getRequestHandler()
if(dev) {
server.on('upgrade', handleRequest)
}
```
- Replaces taskr-babel with taskr-typescript for the `next` package
- Makes sure Node 8+ is used, no unneeded transpilation
- Compile Next.js client side files through babel the same way pages are
- Compile Next.js client side files to esmodules, not commonjs, so that tree shaking works.
- Move error-debug.js out of next-server as it's only used/require in development
- Drop ansi-html as dependency from next-server
- Make next/link esmodule (for tree-shaking)
- Make next/router esmodule (for tree-shaking)
- add typescript compilation to next-server
- Remove last remains of Flow
- Move hoist-non-react-statics to next, out of next-server
- Move htmlescape to next, out of next-server
- Remove runtime-corejs2 from next-server
