TypeScript · Narrowing and unions

instanceof guard

Narrows to a class at runtime. Catch values are unknown because anything can be thrown.

Syntax

if (error instanceof Error)

Example

try {
  JSON.parse("{bad");
} catch (error) {
  if (error instanceof Error) console.log(error.message);
}

Reference pages are the quick answer. The course explains the why, shows the full example and ends with a challenge.