defineAction

Typed action contract API from @zapaction/core.

defineAction

defineAction validates input/output at runtime and keeps static typing across server and client usage.

Signature

packages/core/src/defineAction.ts

export function defineAction<TInput, TOutput, TContext = unknown>(
  options: DefineActionOptions<TInput, TOutput, TContext>
): DefinedAction<TInput, TOutput>

Options

Option	Type	Required	Notes
input	ZodType<TInput>	Yes	Runtime input validation
output	ZodType<TOutput>	No	Runtime output validation
name	string	No	Used by logger
tags	readonly string[]	No	Passed to revalidateTags
beforeAction	(args) => void | Promise<void>	No	Runs before handler
afterAction	(args) => TOutput | void | Promise<TOutput | void>	No	Runs after handler, may override result
handler	({ input, ctx }) => Promise<TOutput>	Yes	Main implementation

Example

app/actions.ts

import { defineAction } from "@zapaction/core";
import { z } from "zod";

export const updateTodo = defineAction({
  name: "updateTodo",
  input: z.object({ id: z.string(), done: z.boolean() }),
  output: z.object({ id: z.string(), done: z.boolean() }),
  tags: ["todos"],
  handler: async ({ input }) => ({
    id: input.id,
    done: input.done
  })
});

Failure modes

• Missing context factory throws a runtime error from resolveActionContext.
• Invalid input/output throws Zod validation errors.
• Empty tags are ignored by server revalidation.