AI is no longer a back-end-only topic. It’s showing up in UIs—from autocomplete to smart assistants. This post shows how to build a simple chatbot UI that talks to a GPT model through an API.

What we’ll build

• A front-end chat interface
• A simple call to a GPT API using fetch
• Handling loading states and errors

1. Setting up the UI

We’ll start with a basic input and message history.

function Chat() {
  const [messages, setMessages] = React.useState([]);
  const [input, setInput] = React.useState("");
  const [loading, setLoading] = React.useState(false);

  const sendMessage = async () => {
    if (!input) return;
    setLoading(true);
    const userMessage = { role: "user", content: input };
    const newMessages = [...messages, userMessage];

    try {
      const res = await fetch("/api/chat", {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({ messages: newMessages }),
      });
      const data = await res.json();
      const botMessage = { role: "assistant", content: data.reply };
      setMessages([...newMessages, botMessage]);
    } catch (err) {
      console.error("Error:", err);
    } finally {
      setLoading(false);
      setInput("");
    }
  };

  return (
    <div>
      <div>
        {messages.map((m, i) => (
          <p key={i}><strong>{m.role}:</strong> {m.content}</p>
        ))}
      </div>
      <input value={input} onChange={e => setInput(e.target.value)} />
      <button onClick={sendMessage} disabled={loading}>Send</button>
    </div>
  );
}

2. Backend handler (Next.js example)

// pages/api/chat.js
export default async function handler(req, res) {
  const messages = req.body.messages;

  const response = await fetch("https://api.openai.com/v1/chat/completions", {
    method: "POST",
    headers: {
      "Authorization": `Bearer YOUR_API_KEY`,
      "Content-Type": "application/json"
    },
    body: JSON.stringify({
      model: "gpt-3.5-turbo",
      messages
    })
  });

  const data = await response.json();
  res.status(200).json({ reply: data.choices[0].message.content });
}

3. Final thoughts

This is just the start. You could:

• Add streaming responses
• Save chat history
• Support tools or actions with function calling

Using AI in the front-end opens a lot of creative space. From simple assistants to personalized content, the line between static UI and smart UI keeps blurring.