rsnext/UPGRADING.md

# Migrating from v8 to v9

## Breaking Changes

#### `@zeit/next-typescript` is no longer necessary

Next.js will now ignore usage `@zeit/next-typescript` and warn you to remove it. Please remove this plugin from your `next.config.js`.

Remove references to `@zeit/next-typescript/babel` from your custom `.babelrc` (if present).

Usage of [`fork-ts-checker-webpack-plugin`](https://github.com/Realytics/fork-ts-checker-webpack-plugin/issues) should also be removed from your `next.config.js`.

TypeScript Definitions are published with the `next` package, so you need to uninstall `@types/next` as they would conflict.

The following types are different:

> This list was created by the community to help you upgrade, if you find other differences please send a pull-request to this list to help other users.

From:
```tsx
import { NextContext } from "next";
import { NextAppContext } from "next/app";
import { NextDocumentContext } from "next/document";
```
to
```tsx
import { NextPageContext } from "next";
import { AppContext } from "next/app";
import { DocumentContext } from "next/document";
```

#### The `config` key is now a special export on a page

You may no longer export a custom variable named `config` from a page (i.e. `export { config }` / `export const config ...`).
This exported variable is now used to specify page-level Next.js configuration like Opt-in AMP and API Route features.

You must rename a non-Next.js-purposed `config` export to something different.

#### `next/dynamic` no longer renders "loading..." by default while loading

Dynamic components will not render anything by default while loading. You can still customize this behavior by setting the `loading` property:

```jsx
import dynamic from 'next/dynamic'

const DynamicComponentWithCustomLoading = dynamic(
  () => import('../components/hello2'),
  {
    loading: () => <p>Loading</p>,
  }
)
```

#### `withAmp` has been removed in favor of an exported configuration object

Next.js now has the concept of page-level configuration, so the `withAmp` higher-order component has been removed for consistency.

This change can be **automatically migrated by running the following commands in the root of your Next.js project:**

```bash
curl -L https://github.com/zeit/next-codemod/archive/master.tar.gz | tar -xz --strip=2 next-codemod-master/transforms/withamp-to-config.js npx jscodeshift -t ./withamp-to-config.js pages/**/*.js
```

To perform this migration by hand, or view what the codemod will produce, see below:

**Before**

```jsx
import { withAmp } from 'next/amp'

function Home() {
  return <h1>My AMP Page</h1>
}

export default withAmp(Home)
// or
export default withAmp(Home, { hybrid: true })
```

**After**

```jsx
export default function Home() {
  return <h1>My AMP Page</h1>
}

export const config = {
  amp: true,
  // or
  amp: 'hybrid',
}
```

#### `next export` no longer exports pages as `index.html`

Previously, exporting `pages/about.js` would result in `out/about/index.html`. This behavior has been changed to result in `out/about.html`.

You can revert to the previous behavior by creating a `next.config.js` with the following content:

```js
// next.config.js
module.exports = {
  exportTrailingSlash: true,
}
```

## Deprecated Features

#### `next/dynamic` has deprecated loading multiple modules at once

The ability to load multiple modules at once has been deprecated in `next/dynamic` to be closer to React's implementation (`React.lazy` and `Suspense`).

Updating code that relies on this behavior is relatively straightforward! We've provided an example of a before/after to help you migrate your application:

**Before**

```jsx
import dynamic from 'next/dynamic'

const HelloBundle = dynamic({
  modules: () => {
    const components = {
      Hello1: () => import('../components/hello1').then(m => m.default),
      Hello2: () => import('../components/hello2').then(m => m.default),
    }

    return components
  },
  render: (props, { Hello1, Hello2 }) => (
    <div>
      <h1>{props.title}</h1>
      <Hello1 />
      <Hello2 />
    </div>
  ),
})

function DynamicBundle() {
  return <HelloBundle title="Dynamic Bundle" />
}

export default DynamicBundle
```

**After**

```jsx
import dynamic from 'next/dynamic'

const Hello1 = dynamic(() => import('../components/hello1'))
const Hello2 = dynamic(() => import('../components/hello2'))

function HelloBundle({ title }) {
  return (
    <div>
      <h1>{title}</h1>
      <Hello1 />
      <Hello2 />
    </div>
  )
}

function DynamicBundle() {
  return <HelloBundle title="Dynamic Bundle" />
}

export default DynamicBundle
```