Functional Error Handling with Result Monads

Snippet

Functional Error Handling with Result Monads

By replacing traditional try-catch blocks with a Result type, you enforce exhaustive error checking at compile time. This pattern is especially useful in Next.js Server Actions to ensure that all failure modes are explicitly handled before sending a response back to the client.

snippet.js
javascript
type Result<T, E = Error> = { ok: true; value: T } | { ok: false; error: E };
 
async function safeFetchUser(id: string): Promise<Result<User>> {
  try {
    const user = await db.users.findUnique({ where: { id } });
    if (!user) return { ok: false, error: new Error('User not found') };
    return { ok: true, value: user };
  } catch (e) {
    return { ok: false, error: e as Error };
  }
}
 
const response = await safeFetchUser('123');
if (response.ok) { console.log(response.value); }

nextjs

Breakdown

type Result<T, E = Error> = ...

Defines a union type representing either a successful computation or a failure.

if (!user) return { ok: false, error: ... };

Explicitly returns an error state instead of throwing, making the failure part of the API contract.

if (response.ok) { ... }

Uses TypeScript's type narrowing to safely access the value only when the operation succeeded.

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Functional Error Handling with Result Monads

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