useOptimisticAction

info

useOptimisticAction does not wait for the action to finish execution before returning the optimistic data. It is then synced with the real result from server when the action has finished its execution. If you need to perform normal mutations, use useAction instead.

Let's say you have some todos in your database and want to add a new one. The following example shows how you can use useOptimisticAction to add a new todo item optimistically.

Example

1. Define a new action called addTodo, that takes a Todo object as input:

"use server";

import { action } from "@/lib/safe-action";
import { revalidatePath } from "next/cache";
import { z } from "zod";

const schema = z.object({
  id: z.string().uuid(),
  body: z.string().min(1),
  completed: z.boolean(),
});

export type Todo = z.infer<typeof schema>;

let todos: Todo[] = [];
export const getTodos = async () => todos;

export const addTodo = action
  .metadata({ actionName: "" })
  .schema(schema)
  .action(async ({ parsedInput }) => {
    await new Promise((res) => setTimeout(res, 500));

    todos.push(parsedInput);

    // This Next.js function revalidates the provided path.
    // More info here: https://nextjs.org/docs/app/api-reference/functions/revalidatePath
    revalidatePath("/optimistic-hook");

    return {
      createdTodo: parsedInput,
    };
  });

2. Then, in the parent Server Component, you need to pass the current todos state to the Client Component:

import { getTodos } from "./addtodo-action";

export default function Home() {
  return (
    <main>
      {/* Here we pass current todos to the Client Component.
      This is updated on the server every time the action is executed, since we
      used `revalidatePath()` inside action's server code. */}
      <TodosBox todos={getTodos()} />
    </main>
  );
}

3. Finally, in your Client Component, you can use it like this:

"use client";

import { useOptimisticAction } from "next-safe-action/hooks";
import { addTodo, type Todo } from "@/app/addtodo-action";

type Props = {
  todos: Todo[];
};

export default function TodosBox({ todos }: Props) {
  const { execute, result, optimisticState } = useOptimisticAction(
    addTodo,
    {
      currentState: { todos }, // gets passed from Server Component
      updateFn: (state, newTodo) => {
        return { 
          todos: [...state.todos, newTodo] 
        };
      }
    }
  );

  return (
    <div>
      <button
        onClick={() => {
          // Here we execute the action. The input is also passed to `updateFn` as the second argument,
          // in this case `newTodo`.
          execute({ id: crypto.randomUUID(), body: "New Todo", completed: false });
        }}>
        Add todo
      </button>
      {/* Optimistic state gets updated immediately, it doesn't wait for the server to respond. */}
      <pre>Optimistic state: {optimisticState}</pre>
    </div>
  );
}

useOptimisticAction arguments

useOptimisticAction has the following arguments:

Name	Type	Purpose
safeActionFn	HookSafeActionFn	This is the action that will be called when you use execute from hook's return object.
utils	{ currentState: State; updateFn: (state: State, input: InferIn<S>) => State } & HookCallbacks	Object with required currentState, updateFn and optional callbacks. See below for more information.

utils properties in detail:

Name	Type	Purpose
currentState	State (generic)	An optimistic state setter. This value should come from the parent Server Component.
updateFn	(state: State, input: InferIn<S>) => State	When you call the action via execute, this function determines how the optimistic state update is performed. Basically, here you define what happens immediately after execute is called, and before the actual result comes back from the server (after revalidation).
{ onExecute?, onSuccess?, onError?, onSettled? }	HookCallbacks	Optional callbacks. More information about them here.

useOptimisticAction return object

useOptimisticAction returns an object with the following properties:

Name	Type	Purpose
execute	(input: InferIn<S>) => void	An action caller with no return. The input is the same as the safe action you passed to the hook.
input	InferIn<S> | undefined	The input passed to the execute function.
result	HookResult	When the action gets called via execute, this is the result object.
optimisticState	State	This contains the state that gets updated immediately after execute is called, with the behavior you defined in the updateFn function. The initial state is what you provided to the hook via currentState argument. If an error occurs during action execution, the optimisticState reverts to the state that it had pre-last-last action execution.
reset	() => void	Programmatically reset input and result object with this function.
status	HookActionStatus	The action current status.
isIdle	boolean	True if the action status is idle.
isExecuting	boolean	True if the action status is executing.
hasSucceeded	boolean	True if the action status is hasSucceeded.
hasErrored	boolean	True if the action status is hasErrored.

Explore a working example here.