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action

A server-side function that handles data mutations (form submissions, API calls) for a route.

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Signature

export function action(args: ActionFunctionArgs): Promise<Response | Data> | Response | Data
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args
ActionFunctionArgs
required
Arguments passed to the action function
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return
Response | Data
Can return:
  • A Response object (redirect, json, etc.)
  • Plain data (accessible via useActionData())
  • A Promise resolving to either

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Basic Example

// app/routes/projects.new.tsx
import { Form, redirect, useActionData } from "react-router";

export async function action({ request }: Route.ActionArgs) {
  const formData = await request.formData();
  const project = await createProject({
    name: formData.get("name"),
    description: formData.get("description")
  });

  return redirect(`/projects/${project.id}`);
}

export default function NewProject() {
  return (
    <Form method="post">
      <input name="name" required />
      <textarea name="description" />
      <button type="submit">Create Project</button>
    </Form>
  );
}

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Handling Form Data

export async function action({ request }: Route.ActionArgs) {
  const formData = await request.formData();
  
  // Get individual fields
  const title = formData.get("title");
  const published = formData.get("published") === "on";
  
  // Get all values for a multi-select
  const tags = formData.getAll("tags");
  
  // Convert to object
  const data = Object.fromEntries(formData);
  
  await updatePost(data);
  return { success: true };
}

​
Validation and Error Handling

import { useActionData } from "react-router";

type ActionData = {
  errors?: {
    email?: string;
    password?: string;
  };
};

export async function action({ request }: Route.ActionArgs) {
  const formData = await request.formData();
  const email = formData.get("email");
  const password = formData.get("password");

  const errors: ActionData["errors"] = {};
  
  if (!email?.includes("@")) {
    errors.email = "Invalid email address";
  }
  
  if (!password || password.length < 8) {
    errors.password = "Password must be at least 8 characters";
  }

  if (Object.keys(errors).length > 0) {
    return { errors };
  }

  await createUser({ email, password });
  return redirect("/dashboard");
}

export default function Signup() {
  const actionData = useActionData<typeof action>();

  return (
    <Form method="post">
      <div>
        <input name="email" type="email" />
        {actionData?.errors?.email && (
          <span className="error">{actionData.errors.email}</span>
        )}
      </div>
      <div>
        <input name="password" type="password" />
        {actionData?.errors?.password && (
          <span className="error">{actionData.errors.password}</span>
        )}
      </div>
      <button type="submit">Sign Up</button>
    </Form>
  );
}

​
JSON Submissions

export async function action({ request }: Route.ActionArgs) {
  const data = await request.json();
  
  const result = await updateSettings(data);
  
  return Response.json({ result }, { status: 200 });
}

// From the client
fetch("/settings", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ theme: "dark" })
});

​
Multiple Actions with Intent

export async function action({ request }: Route.ActionArgs) {
  const formData = await request.formData();
  const intent = formData.get("intent");

  switch (intent) {
    case "delete": {
      const id = formData.get("id");
      await deletePost(id);
      return { deleted: id };
    }
    case "publish": {
      const id = formData.get("id");
      await publishPost(id);
      return { published: id };
    }
    default: {
      throw new Error(`Unknown intent: ${intent}`);
    }
  }
}

export default function Post() {
  return (
    <>
      <Form method="post">
        <input type="hidden" name="intent" value="publish" />
        <input type="hidden" name="id" value={post.id} />
        <button type="submit">Publish</button>
      </Form>
      
      <Form method="post">
        <input type="hidden" name="intent" value="delete" />
        <input type="hidden" name="id" value={post.id} />
        <button type="submit">Delete</button>
      </Form>
    </>
  );
}

​
File Uploads

export async function action({ request }: Route.ActionArgs) {
  const formData = await request.formData();
  const file = formData.get("avatar") as File;

  if (!file || file.size === 0) {
    return { error: "Please select a file" };
  }

  if (!file.type.startsWith("image/")) {
    return { error: "File must be an image" };
  }

  const buffer = await file.arrayBuffer();
  const url = await uploadToStorage(buffer, file.type);

  await updateUserAvatar(url);
  return { success: true };
}

​
Best Practices

By default, loaders are automatically revalidated after actions. This ensures your UI stays in sync:
export async function loader({ params }: Route.LoaderArgs) {
  return { post: await getPost(params.id) };
}

export async function action({ params, request }: Route.ActionArgs) {
  const formData = await request.formData();
  await updatePost(params.id, Object.fromEntries(formData));
  
  // Loader automatically revalidates, UI updates
  return { success: true };
}
Return data instead of redirecting to enable optimistic updates:
export async function action({ request }: Route.ActionArgs) {
  const formData = await request.formData();
  const comment = await createComment(Object.fromEntries(formData));
  
  // Return data so UI can update immediately
  return { comment };
}
For create/delete operations, redirect to the appropriate page:
import { redirect } from "react-router";

export async function action({ request }: Route.ActionArgs) {
  const formData = await request.formData();
  const post = await createPost(Object.fromEntries(formData));
  
  // Redirect to the new post
  return redirect(`/posts/${post.id}`);
}
Throw responses for error boundaries or return errors for inline display:
export async function action({ request }: Route.ActionArgs) {
  try {
    const formData = await request.formData();
    await processPayment(formData);
    return redirect("/success");
  } catch (error) {
    if (error.code === "CARD_DECLINED") {
      // Return error for inline display
      return { error: "Card was declined" };
    }
    // Throw for error boundary
    throw error;
  }
}

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See Also

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