This PR aims at replacing next-server/lib/event-emitter.js by mitt.
Fix https://github.com/zeit/next.js/issues/4908
event-emitter.js is ~400 bytes gzipped vs mitt is 200 bytes
Resolves#4055
Credit: https://github.com/zeit/next.js/pull/5095
I didn't use the ignore webpack plugin from the original PR and tested bundle size with https://github.com/zeit/next.js/pull/5339 - seems to be safe on that front.
Was able to get tests to pass locally, unsure of what goes wrong in CI 🤷♂️
**Questions**
1) The initial PR didn't include changes to `next-server/lib/router` in `getRouteInfo()`. Should the same changes be made within?
2) Should we add a test for rendering a component created via `forwardRef()`?
`component-with-forwardedRef`:
```javascript
export default React.forwardRef((props, ref) => <span {...props} forwardedRef={ref}>This is a component with a forwarded ref</span>);
```
some test:
```javascript
test('renders from forwardRef', async () => {
const $ = await get$('/component-with-forwardedRef')
const span = $('span')
expect(span.text()).toMatch(/This is a component with a forwarded ref/)
})
```
- 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
