Convex React Client Guide

Complete React client guidelines for Convex, including hooks, real-time updates, optimistic updates, and best practices for building reactive UIs.

---

Basic React Integration

Complete Example

import React, { useState } from "react";
import { useMutation, useQuery } from "convex/react";
import { api } from "../convex/_generated/api";

export default function App() {
  const messages = useQuery(api.messages.list) || [];

  const [newMessageText, setNewMessageText] = useState("");
  const sendMessage = useMutation(api.messages.send);

  const [name] = useState(() => "User " + Math.floor(Math.random() * 10000));

  async function handleSendMessage(event: React.FormEvent) {
    event.preventDefault();
    await sendMessage({ body: newMessageText, author: name });
    setNewMessageText("");
  }

  return (
    <main>
      <h1>Convex Chat</h1>
      <p className="badge">
        <span>{name}</span>
      </p>
      <ul>
        {messages.map((message) => (
          <li key={message._id}>
            <span>{message.author}:</span>
            <span>{message.body}</span>
            <span>{new Date(message._creationTime).toLocaleTimeString()}</span>
          </li>
        ))}
      </ul>
      <form onSubmit={handleSendMessage}>
        <input
          value={newMessageText}
          onChange={(event) => setNewMessageText(event.target.value)}
          placeholder="Write a message..."
        />
        <button type="submit" disabled={!newMessageText}>
          Send
        </button>
      </form>
    </main>
  );
}

---

useQuery Hook

Real-time Updates

The

useQuery()

hook is live-updating! It causes the React component to rerender automatically when data changes. Convex is a perfect fit for collaborative, live-updating websites.

Return Values

• undefined

  - Query is loading

• null

  - Query returned null (e.g., user not found)

• data

  - Query returned data

function UserProfile({ userId }: { userId: Id<"users"> }) {
  const user = useQuery(api.users.get, { userId });

  // Loading state
  if (user === undefined) {
    return <div>Loading...</div>;
  }

  // Not found
  if (user === null) {
    return <div>User not found</div>;
  }

  // Data loaded
  return <div>{user.name}</div>;
}

---

Conditional Queries with "skip"

CRITICAL: Never Use Hooks Conditionally

// WRONG - Will cause React hook errors!
const avatarUrl = profile?.avatarId
  ? useQuery(api.profiles.getAvatarUrl, { storageId: profile.avatarId })
  : null;

// CORRECT - Use "skip" to conditionally skip the query
const avatarUrl = useQuery(
  api.profiles.getAvatarUrl,
  profile?.avatarId ? { storageId: profile.avatarId } : "skip"
);

More Examples

function Dashboard() {
  const user = useQuery(api.auth.loggedInUser);

  // Skip queries until we have user data
  const userPosts = useQuery(
    api.posts.getByUser,
    user ? { userId: user._id } : "skip"
  );

  const userSettings = useQuery(
    api.settings.get,
    user ? { userId: user._id } : "skip"
  );

  if (user === undefined) {
    return <Loading />;
  }

  if (user === null) {
    return <LoginPrompt />;
  }

  return (
    <div>
      <PostList posts={userPosts || []} />
      <Settings settings={userSettings} />
    </div>
  );
}

---

useMutation Hook

Basic Usage

function CreatePost() {
  const createPost = useMutation(api.posts.create);
  const [title, setTitle] = useState("");
  const [content, setContent] = useState("");
  const [isSubmitting, setIsSubmitting] = useState(false);

  async function handleSubmit(e: React.FormEvent) {
    e.preventDefault();
    setIsSubmitting(true);

    try {
      await createPost({ title, content });
      setTitle("");
      setContent("");
    } catch (error) {
      console.error("Failed to create post:", error);
    } finally {
      setIsSubmitting(false);
    }
  }

  return (
    <form onSubmit={handleSubmit}>
      <input
        value={title}
        onChange={(e) => setTitle(e.target.value)}
        placeholder="Title"
        disabled={isSubmitting}
      />
      <textarea
        value={content}
        onChange={(e) => setContent(e.target.value)}
        placeholder="Content"
        disabled={isSubmitting}
      />
      <button type="submit" disabled={isSubmitting || !title || !content}>
        {isSubmitting ? "Creating..." : "Create Post"}
      </button>
    </form>
  );
}

---

useAction Hook

import { useAction } from "convex/react";
import { api } from "../convex/_generated/api";

function AIChat() {
  const generateResponse = useAction(api.ai.generateResponse);
  const [prompt, setPrompt] = useState("");
  const [response, setResponse] = useState("");
  const [isLoading, setIsLoading] = useState(false);

  async function handleSubmit(e: React.FormEvent) {
    e.preventDefault();
    setIsLoading(true);

    try {
      const result = await generateResponse({ prompt });
      setResponse(result);
    } catch (error) {
      console.error("AI generation failed:", error);
    } finally {
      setIsLoading(false);
    }
  }

  return (
    <div>
      <form onSubmit={handleSubmit}>
        <input
          value={prompt}
          onChange={(e) => setPrompt(e.target.value)}
          placeholder="Ask AI..."
          disabled={isLoading}
        />
        <button type="submit" disabled={isLoading || !prompt}>
          {isLoading ? "Thinking..." : "Ask"}
        </button>
      </form>
      {response && <p>{response}</p>}
    </div>
  );
}

---

Importing the API Object

When writing a UI component and you want to use a Convex function, you MUST import the

api

object:

import { api } from "../convex/_generated/api";

You can use the

api

object to call any public Convex function.

Always make sure:

1. The functions you are calling are defined in the

   convex/

   directory
2. Use the

   api

   object for public functions
3. You are using the correct arguments for convex functions
4. If arguments are not optional, make sure they are not null

---

Pagination with usePaginatedQuery

import { usePaginatedQuery } from "convex/react";
import { api } from "../convex/_generated/api";

function InfiniteMessageList({ channelId }: { channelId: Id<"channels"> }) {
  const { results, status, loadMore } = usePaginatedQuery(
    api.messages.list,
    { channelId },
    { initialNumItems: 20 }
  );

  return (
    <div>
      {results.map((message) => (
        <div key={message._id}>{message.content}</div>
      ))}

      {status === "CanLoadMore" && (
        <button onClick={() => loadMore(20)}>Load More</button>
      )}

      {status === "LoadingMore" && <div>Loading...</div>}

      {status === "Exhausted" && <div>No more messages</div>}
    </div>
  );
}

---

Optimistic Updates

import { useMutation, useQuery } from "convex/react";
import { api } from "../convex/_generated/api";

function TodoList() {
  const todos = useQuery(api.todos.list) || [];
  const toggleTodo = useMutation(api.todos.toggle).withOptimisticUpdate(
    (localStore, args) => {
      const currentTodos = localStore.getQuery(api.todos.list);
      if (currentTodos !== undefined) {
        const updatedTodos = currentTodos.map((todo) =>
          todo._id === args.id
            ? { ...todo, completed: !todo.completed }
            : todo
        );
        localStore.setQuery(api.todos.list, {}, updatedTodos);
      }
    }
  );

  return (
    <ul>
      {todos.map((todo) => (
        <li key={todo._id}>
          <input
            type="checkbox"
            checked={todo.completed}
            onChange={() => toggleTodo({ id: todo._id })}
          />
          {todo.title}
        </li>
      ))}
    </ul>
  );
}

---

Error Handling

function PostForm() {
  const createPost = useMutation(api.posts.create);
  const [error, setError] = useState<string | null>(null);

  async function handleSubmit(data: FormData) {
    setError(null);

    try {
      await createPost({
        title: data.get("title") as string,
        content: data.get("content") as string,
      });
    } catch (e) {
      if (e instanceof Error) {
        setError(e.message);
      } else {
        setError("An unexpected error occurred");
      }
    }
  }

  return (
    <form action={handleSubmit}>
      {error && <div className="error">{error}</div>}
      {/* form fields */}
    </form>
  );
}

---

Loading States Pattern

function DataComponent() {
  const data = useQuery(api.data.get);

  // Pattern 1: Simple loading check
  if (data === undefined) {
    return <Skeleton />;
  }

  // Pattern 2: With null check
  if (data === null) {
    return <NotFound />;
  }

  return <DataView data={data} />;
}

---

File Upload Pattern

function ImageUploader() {
  const generateUploadUrl = useMutation(api.files.generateUploadUrl);
  const saveFile = useMutation(api.files.save);
  const [uploading, setUploading] = useState(false);

  async function handleFileChange(e: React.ChangeEvent<HTMLInputElement>) {
    const file = e.target.files?.[0];
    if (!file) return;

    setUploading(true);

    try {
      // Step 1: Get upload URL
      const uploadUrl = await generateUploadUrl();

      // Step 2: Upload file
      const result = await fetch(uploadUrl, {
        method: "POST",
        headers: { "Content-Type": file.type },
        body: file,
      });

      if (!result.ok) {
        throw new Error("Upload failed");
      }

      const { storageId } = await result.json();

      // Step 3: Save reference to database
      await saveFile({ storageId, fileName: file.name });

    } catch (error) {
      console.error("Upload error:", error);
    } finally {
      setUploading(false);
    }
  }

  return (
    <input
      type="file"
      onChange={handleFileChange}
      disabled={uploading}
    />
  );
}

---

Image Display with Storage URLs

function ImageGallery() {
  const images = useQuery(api.images.list) || [];

  return (
    <div className="grid grid-cols-3 gap-4">
      {images.map((image) => (
        <ImageWithUrl key={image._id} storageId={image.storageId} />
      ))}
    </div>
  );
}

function ImageWithUrl({ storageId }: { storageId: Id<"_storage"> }) {
  const url = useQuery(api.files.getUrl, { storageId });

  if (url === undefined) {
    return <div className="animate-pulse bg-gray-200 h-48" />;
  }

  if (url === null) {
    return <div>Image not found</div>;
  }

  return <img src={url} alt="" className="w-full h-48 object-cover" />;
}

---

Provider Setup

// main.tsx or _app.tsx
import { ConvexProvider, ConvexReactClient } from "convex/react";
import { ConvexAuthProvider } from "@convex-dev/auth/react";

const convex = new ConvexReactClient(import.meta.env.VITE_CONVEX_URL);

function App() {
  return (
    <ConvexAuthProvider client={convex}>
      <YourApp />
    </ConvexAuthProvider>
  );
}

---

Best Practices

1. Never Call Hooks Conditionally

// WRONG
if (isLoggedIn) {
  const data = useQuery(api.data.get);
}

// CORRECT
const data = useQuery(api.data.get, isLoggedIn ? {} : "skip");

2. Handle All States

function DataDisplay() {
  const data = useQuery(api.data.get);

  // Always handle: undefined (loading), null (not found), and data
  if (data === undefined) return <Loading />;
  if (data === null) return <NotFound />;
  return <Content data={data} />;
}

3. Use TypeScript Properly

import { Id } from "../convex/_generated/dataModel";

interface Props {
  userId: Id<"users">;  // Use Id<> type, not string
}

4. Avoid Prop Drilling with Queries

// Instead of passing data through many components,
// query it where needed
function DeepNestedComponent({ itemId }: { itemId: Id<"items"> }) {
  // Query directly in the component that needs it
  const item = useQuery(api.items.get, { id: itemId });
  // ...
}

5. Do NOT Use External UI Libraries Unless Specified

If you want to use a UI element, you MUST create it. DO NOT use external libraries like Shadcn/UI unless explicitly asked.

6. Do NOT Use sharp for Image Compression

Always use

canvas

for image compression, not

sharp

.