Add Convex example (vercel#38129)

Adds an example using [Convex](https://convex.dev/).

## Documentation / Examples

- [x] Make sure the linting passes by running `pnpm lint`
- [x] The examples guidelines are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)


Co-authored-by: Balázs Orbán <[email protected]>

Author: thomasballinger

examples/convex/.gitignore

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+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
+# dependencies
+/node_modules
+/.pnp
+.pnp.js
+
+# testing
+/coverage
+
+# next.js
+/.next/
+/out/
+
+# production
+/build
+
+# misc
+.DS_Store
+*.pem
+
+# debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# local env files
+.env.local
+.env.development.local
+.env.test.local
+.env.production.local
+
+# vercel
+.vercel
+
+# convex
+convex/_generated
+
+# typescript
+*.tsbuildinfo

examples/convex/README.md

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+# Convex
+
+This example demonstrates the Convex global state management framework.
+
+## Deploy your own
+
+Deploy the example using [Vercel](https://vercel.com?utm_source=github&utm_medium=readme&utm_campaign=next-example):
+
+[![Deploy with Vercel](https://vercel.com/button)](https://vercel.com/new/git/external?repository-url=https://github.com/vercel/next.js/tree/canary/examples/convex&project-name=convex&repository-name=convex)
+
+## How to use
+
+Execute [`create-next-app`](https://github.com/vercel/next.js/tree/canary/packages/create-next-app) with [npm](https://docs.npmjs.com/cli/init), [Yarn](https://yarnpkg.com/lang/en/docs/cli/create/), or [pnpm](https://pnpm.io) to bootstrap the example:
+
+```bash
+npx create-next-app --example with-convex with-convex-app
+# or
+yarn create next-app --example with-convex with-convex-app
+# or
+pnpm create next-app --example with-convex with-convex-app
+```
+
+After creating a [Convex account](https://www.convex.dev) and getting a beta key,
+
+```bash
+npx convex init --beta-key <your beta key>
+```
+
+Next, push the Convex functions for this project.
+
+```bash
+npx convex push
+```
+
+Deploy it to the cloud with [Vercel](https://vercel.com/new?utm_source=github&utm_medium=readme&utm_campaign=next-example) ([Documentation](https://nextjs.org/docs/deployment)).

examples/convex/convex/README.md

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+# Welcome to your functions directory
+
+Write your convex functions in this directory.
+
+A query function (how you read data) looks like this:
+
+```typescript
+// getCounter.ts
+import { query } from './_generated/server'
+
+export default query(async ({ db }): Promise<number> => {
+  const counterDoc = await db.table('counter_table').first()
+  console.log('Got stuff')
+  if (counterDoc === null) {
+    return 0
+  }
+  return counterDoc.counter
+})
+```
+
+A mutation function (how you write data) looks like this:
+
+```typescript
+// incrementCounter.ts
+import { mutation } from './_generated/server'
+
+export default mutation(async ({ db }, increment: number) => {
+  let counterDoc = await db.table('counter_table').first()
+  if (counterDoc === null) {
+    counterDoc = {
+      counter: increment,
+    }
+    db.insert('counter_table', counterDoc)
+  } else {
+    counterDoc.counter += increment
+    db.replace(counterDoc._id, counterDoc)
+  }
+  // Like console.log but relays log messages from the server to client.
+  console.log(`Value of counter is now ${counterDoc.counter}`)
+})
+```
+
+The convex cli is your friend. See everything it can do by running
+`npx convex -h` in your project root directory. To learn more, launch the docs
+with `npx convex docs`.

examples/convex/convex/getCounter.ts

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+import { query } from './_generated/server'
+
+export default query(async ({ db }, counterName: string): Promise<number> => {
+  const counterDoc = await db
+    .table('counter_table')
+    .filter((q) => q.eq(q.field('name'), counterName))
+    .first()
+  console.log('Got stuff')
+  if (counterDoc === null) {
+    return 0
+  }
+  return counterDoc.counter
+})

examples/convex/convex/incrementCounter.ts

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+import { mutation } from './_generated/server'
+
+export default mutation(
+  async ({ db }, counterName: string, increment: number) => {
+    let counterDoc = await db
+      .table('counter_table')
+      .filter((q) => q.eq(q.field('name'), counterName))
+      .first()
+    if (counterDoc === null) {
+      counterDoc = {
+        name: counterName,
+        counter: increment,
+      }
+      db.insert('counter_table', counterDoc)
+    } else {
+      counterDoc.counter += increment
+      db.replace(counterDoc._id, counterDoc)
+    }
+    // Like console.log but relays log messages from the server to client.
+    console.log(`Value of counter is now ${counterDoc.counter}`)
+  }
+)

examples/convex/next-env.d.ts

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+/// <reference types="next" />
+/// <reference types="next/image-types/global" />
+
+// NOTE: This file should not be edited
+// see https://nextjs.org/docs/basic-features/typescript for more information.

examples/convex/package.json

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+{
+  "private": true,
+  "scripts": {
+    "dev": "next dev",
+    "build": "next build",
+    "start": "next start"
+  },
+  "dependencies": {
+    "next": "latest",
+    "react": "^18.2.0",
+    "react-dom": "^18.2.0",
+    "convex-dev": "0.1.4"
+  },
+  "devDependencies": {
+    "@types/node": "~16.11.12",
+    "@types/react": "17.0.45",
+    "@types/react-dom": "17.0.17",
+    "typescript": "^4.7.3"
+  }
+}

examples/convex/pages/_app.tsx

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+import '../styles/globals.css'
+import type { AppProps } from 'next/app'
+
+import { ConvexProvider, ConvexReactClient } from 'convex-dev/react'
+import convexConfig from '../convex.json'
+const convex = new ConvexReactClient(convexConfig.origin)
+
+function MyApp({ Component, pageProps }: AppProps) {
+  return (
+    <ConvexProvider client={convex}>
+      <Component {...pageProps} />;
+    </ConvexProvider>
+  )
+}
+
+export default MyApp

examples/convex/pages/index.tsx

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+import type { NextPage } from 'next'
+import Head from 'next/head'
+import Image from 'next/image'
+import styles from '../styles/Home.module.css'
+import { useQuery, useMutation } from '../convex/_generated/react'
+import { useCallback } from 'react'
+
+const Home: NextPage = () => {
+  const counter = useQuery('getCounter', 'clicks') ?? 0
+  const increment = useMutation('incrementCounter')
+  const incrementByOne = useCallback(() => increment('clicks', 1), [increment])
+
+  return (
+    <div className={styles.container}>
+      <Head>
+        <title>Next.js with Convex</title>
+        <meta name="description" content="Generated by create next app" />
+        <link rel="icon" href="/favicon.ico" />
+      </Head>
+
+      <main className={styles.main}>
+        <h1 className={styles.title}>
+          Welcome to <a href="https://nextjs.org">Next.js</a> with{' '}
+          <a href="https://convex.dev">Convex</a>
+        </h1>
+
+        <p className={styles.description}>
+          {"Here's the counter:"} {counter}
+        </p>
+        <button className={styles.button} onClick={incrementByOne}>
+          Add One!
+        </button>
+      </main>
+
+      <footer className={styles.footer}>
+        <a
+          href="https://www.convex.dev/"
+          target="_blank"
+          rel="noopener noreferrer"
+        >
+          Powered by{' '}
+          <span className={styles.logo}>
+            <Image src="/convex.svg" alt="Convex Logo" width={90} height={18} />
+          </span>
+        </a>
+      </footer>
+    </div>
+  )
+}
+
+export default Home