Skip to main content

Convex React

Convex React is the client library enabling your React application to interact with your Convex backend. It allows your frontend code to:

  1. Call your Queries, Mutations and Actions
  2. Upload and display files from File Storage
  3. Authenticate users using Authentication
  4. Implement full text Search over your data

Installation​

Convex React is part of the convex npm package:

npm install convex

Connecting to a backend​

The ConvexReactClient maintains a connection to your Convex backend, and is used by the React hooks described below to call your functions.

First you need to create an instance of the client by giving it your backend deployment URL. See Configuring Deployment URL on how to pass in the right value:

src/index.js
import { ConvexProvider, ConvexReactClient } from "convex/react";
const convex = new ConvexReactClient("https://<domain>.convex.cloud");

And then you make the client available to your app by passing it in to a ConvexProvider wrapping your main component:

src/index.js
reactDOMRoot.render(
  <React.StrictMode>
    <ConvexProvider client={convex}>
      <App />
    </ConvexProvider>
  </React.StrictMode>
);

Fetching data​

Your React app fetches data using the useQuery React hook by calling your queries.

The convex dev command generates this hook for you in the convex/_generated/react.js module to provide better autocompletion in JavaScript and end-to-end type safety in TypeScript:

src/App.js
import { useQuery } from "../convex/_generated/react";

export function App() {
  const data = useQuery("myQuery");
  return data ?? "Loading...";
}

The useQuery hook returns undefined while the data is first loading and afterwards the return value of your query.

Query arguments​

Arguments to your query follow the query name:

src/App.js
export function App() {
  const a = "Hello world";
  const b = 4;
  const data = useQuery("myQuery", { a, b });
  …

Reactivity​

The useQuery hook makes your app automatically reactive: when the underlying data changes in your database, your component rerenders with the new query result.

The first time the hook is used it creates a subscription to your backend for a given query and any arguments you pass in. When your component unmounts, the subscription is cancelled.

Consistency​

Convex React ensures that your application always renders a consistent view of the query results based on a single state of the underlying database.

Imagine a mutation changes some data in the database, and that 2 different useQuery call sites rely on this data. Your app will never render in an inconsistent state where only one of the useQuery call sites reflects the new data.

Editing data​

Your React app edits data using the useMutation React hook by calling your mutations.

The convex dev command generates this hook for you in the convex/_generated/react.js module to provide better autocompletion in JavaScript and end-to-end type safety in TypeScript:

src/App.js
import { useMutation } from "../convex/_generated/react";

export function App() {
  const doSomething = useMutation("doSomething");
  return <button onClick={() => doSomething()}>Click me</button>;
}

The hook returns an async function which performs the call to the mutation.

Mutation arguments​

Arguments to your mutation are passed to the async function returned from useMutation:

src/App.js
export function App() {
  const a = "Hello world";
  const b = 4;
  const doSomething = useMutation("doSomething");
  return <button onClick={() => doSomething({ a, b })}>Click me</button>;
}

Mutation response and error handling​

The mutation can optionally return a value or throw errors, which you can await:

src/App.js
export function App() {
  const doSomething = useMutation("doSomething");
  const onClick = () => {
    async function callBackend() {
      try {
        const result = await doSomething();
      } catch (error) {
        console.error(error);
      }
      console.log(result);
    }
    callBackend();
  };
  return <button onClick={onClick}>Click me</button>;
}

Or handle as a Promise:

src/App.js
export function App() {
  const doSomething = useMutation("doSomething");
  const onClick = () => {
    doSomething()
      .catch(error => {
        console.error(error);
      })
      .then(result => {
        console.log(result);
      });
  };
  return <button onClick={onClick}>Click me</button>;
}

Learn more about Error Handling in functions.

Retries​

Convex React automatically retries mutations until they are confirmed to have been written to the database. The Convex backend ensures that despite multiple retries, every mutation call only executes once.

Additionally, Convex React will warn users if they try to close their browser tab while there are outstanding mutations. This means that when you call a Convex mutation, you can be sure that the user's edits won't be lost.

Optimistic updates​

Convex queries are fully reactive, so all query results will be automatically updated after a mutation. Sometimes you may want to update the UI before the mutation changes propagate back to the client. To accomplish this, you can configure an optimistic update to execute as part of your mutation.

Optimistic updates are temporary, local changes to your query results which are used to make your app more responsive.

See Optimistic Updates on how to configure them.

Calling third-party APIs​

Your React app can read data, call third-party services, and write data with a single backend call using the useAction React hook by calling your actions.

The convex dev command generates this hook for you in the convex/_generated/react.js module to provide better autocompletion in JavaScript and end-to-end type safety in TypeScript:

src/App.js
import { useAction } from "../convex/_generated/react";

export function App() {
  const doSomeAction = useAction("actions/doSomeAction");
  return <button onClick={() => doSomeAction()}>Click me</button>;
}

The hook returns an async function which performs the call to the action.

Action arguments​

Action arguments work exactly the same as mutation arguments.

Action response and error handling​

Action response and error handling work exactly the same as mutation response and error handling.

Actions do not support automatic retries or optimistic updates.

Under the hood​

The ConvexReactClient connects to your Convex deployment by creating a WebSocket. The WebSocket provides a 2-way communication channel over TCP. This allows Convex to push new query results reactively to the client without the client needing to poll for updates.

If the internet connection drops, the client will handle reconnecting and re-establishing the Convex session automatically.