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Narrow Result states

A Result<T, E> is a union of Ok<T, E>, Err<T, E>, and — when awaiting is involved — Pending<T, E>. TypeScript cannot see value or error until you narrow.

Branch on isOk / isErr​

if (result.isOk()) {
	use(result.value);   // T
} else {
	report(result.error); // E
}

Both methods are type guards. Inside the if block, result is narrowed to the matching variant and .value / .error become accessible.

Peel off Pending first​

If you have a Pending, await it — do not try to narrow a Pending directly for .value.

const settled = await pending;
if (settled.isOk()) {
	use(settled.value);
}

isPending exists for rare cases where you hold a union that includes Pending but have not yet awaited — most code should await first and narrow second.

Exhaustive switch with .match​

When you want to handle every branch in one expression, use .match:

const message = result.match({
	ok: (value) => `got ${value}`,
	err: (error) => `failed: ${error.kind}`,
});

See also​