Next.js Pages Router Quickstart

The Vercel AI SDK is a powerful Typescript library designed to help developers build AI-powered applications.

In this quickstart tutorial, you'll build a simple AI-chatbot with a streaming user interface. Along the way, you'll learn key concepts and techniques that are fundamental to using the SDK in your own projects.

If you are unfamiliar with the concepts of Prompt Engineering and HTTP Streaming, you can optionally read these documents first.

Prerequisites

To follow this quickstart, you'll need:

• Node.js 18+ and pnpm installed on your local development machine.
• An OpenAI API key.

If you haven't obtained your OpenAI API key, you can do so by signing up on the OpenAI website.

Setup Your Application

Start by creating a new Next.js application. This command will create a new directory named my-ai-app and set up a basic Next.js application inside it.

pnpm create next-app@latest my-ai-app

Navigate to the newly created directory:

cd my-ai-app

Install dependencies

Install ai and @ai-sdk/openai, Vercel AI SDK's OpenAI provider.

pnpm install ai @ai-sdk/openai zod

Configure OpenAI API Key

Create a .env.local file in your project root and add your OpenAI API Key. This key is used to authenticate your application with the OpenAI service.

touch .env.local

Edit the .env.local file:

OPENAI_API_KEY=xxxxxxxxx

Replace xxxxxxxxx with your actual OpenAI API key.

Create a Route Handler

Create a Route Handler (app/api/chat/route.ts) and add the following code:

import { openai } from '@ai-sdk/openai';
import { StreamingTextResponse, streamText } from 'ai';

// Allow streaming responses up to 30 seconds
export const maxDuration = 30;

export async function POST(req: Request) {
  const { messages } = await req.json();

  const result = await streamText({
    model: openai('gpt-4-turbo'),
    messages,
  });

  return result.toAIStreamResponse();
}

Let's take a look at what is happening in this code:

1. Define an asynchronous POST request and extract messages from the body of the request. The messages variable contains a history of the conversation with you and the chatbot and will provide the chatbot with the necessary context to make the next generation.
2. Call the streamText function which is imported from the ai package. To use this function, you pass it a configuration object that contains a model provider (imported from @ai-sdk/openai) and messages (defined in step 2). You can use pass additional settings in this configuration object to further customise the models behaviour.
3. The streamText function returns a StreamTextResult. This result object contains the toAIStreamResponse function which converts the result to a streamed response object.
4. Return the result to the client to stream the response.

This Route Handler creates a POST request endpint at /api/chat.

Wire up the UI

Now that you have an API route that can query an LLM, it's time to setup your frontend. Vercel AI SDK's UI package abstract the complexity of a chat interface into one hook, useChat.

Update your root page (pages/index.tsx) with the following code to show a list of chat messages and provide a user message input:

import { useChat } from 'ai/react';

export default function Chat() {
  const { messages, input, handleInputChange, handleSubmit } = useChat();
  return (
    <div className="flex flex-col w-full max-w-md py-24 mx-auto stretch">
      {messages.map(m => (
        <div key={m.id} className="whitespace-pre-wrap">
          {m.role === 'user' ? 'User: ' : 'AI: '}
          {m.content}
        </div>
      ))}

      <form onSubmit={handleSubmit}>
        <input
          className="fixed bottom-0 w-full max-w-md p-2 mb-8 border border-gray-300 rounded shadow-xl"
          value={input}
          placeholder="Say something..."
          onChange={handleInputChange}
        />
      </form>
    </div>
  );
}

This page utilizes the useChat hook, which will, by default, use the POST API route you created earlier (/api/chat). The hook provides functions and state for handling user input and form submission. The useChat hook provides multiple utility functions and state variables:

• messages - the current chat messages (an array of objects with id, role, and content properties).
• input - the current value of the user's input field.
• handleInputChange and handleSubmit - functions to handle user interactions (typing into the input field and submitting the form, respectively).
• isLoading - boolean that indicates whether the API request is in progress.

Running Your Application

With that, you have built everything you need for your chatbot! To start your application, use the command:

pnpm run dev

Head to your browser and open http://localhost:3000. You should see an input field. Test it out by entering a message and see the AI chatbot respond in real-time! Vercel AI SDK makes it fast and easy to build AI chat interfaces with Next.js.

Stream Data Alongside Response

Depending on your use case, you may want to stream additional data alongside the model's response. This can be done using StreamData.

Update your Route Handler

Make the following changes to your Route Handler (app/api/chat/route.ts)

import { openai } from '@ai-sdk/openai';
import { streamText, StreamData } from 'ai';

// Allow streaming responses up to 30 seconds
export const maxDuration = 30;

export async function POST(req: Request) {
  const { messages } = await req.json();

  const data = new StreamData();
  data.append({ test: 'value' });

  const result = await streamText({
    model: openai('gpt-4-turbo'),
    messages,
    onFinish() {
      data.close();
    },
  });

  return result.toAIStreamResponse({ data });
}

In this code, you:

1. Create a new instance of StreamData.
2. Append the data you want to stream alongside the model's response.
3. Listen for the onFinish callback on streamText and close the stream data.
4. Pass the data into the toAIStreamResponse method.

Update your frontend

To access this data on the frontend, the useChat hook returns an optional value that stores this data. Update your root route with the following code to render the streamed data:

import { useChat } from 'ai/react';

export default function Chat() {
  const { messages, input, handleInputChange, handleSubmit, data } = useChat();
  return (
    <div className="flex flex-col w-full max-w-md py-24 mx-auto stretch">
      {data && <pre>{JSON.stringify(data, null, 2)}</pre>}
      {messages.map(m => (
        <div key={m.id} className="whitespace-pre-wrap">
          {m.role === 'user' ? 'User: ' : 'AI: '}
          {m.content}
        </div>
      ))}

      <form onSubmit={handleSubmit}>
        <input
          className="fixed bottom-0 w-full max-w-md p-2 mb-8 border border-gray-300 rounded shadow-xl"
          value={input}
          placeholder="Say something..."
          onChange={handleInputChange}
        />
      </form>
    </div>
  );
}

Head back to your browser (http://localhost:3000) and enter a new message. You should see a JSON object appear with the value you sent from your API route!

Where to Next?

You've built an AI chatbot using the Vercel AI SDK! Experiment and extend the functionality of this application further by exploring tool calling or persisting chat history.

If you are looking to leverage the broader capabilities of LLMs, Vercel AI SDK Core provides a comprehensive set of lower-level tools and APIs that will help you unlock a wider range of AI functionalities beyond the chatbot paradigm.