// doc: https://devblogs.microsoft.com/typescript/announcing-typescript-4-0/#unknown-on-catch
try { /* ... */ }
catch (e: unknown) { // <-- note `e` has explicit `unknown` type e.message // errors if (typeof e === "string") { e.toUpperCase() // works, `e` narrowed to string } else if (e instanceof Error) { e.message // works, `e` narrowed to Error } // ... handle other error types
}
// Typescript 4.4 added the ability to make unknown the default on catch variables using the useUnknownInCatchVariables flag.

class MyError extends Error { constructor(message: string) { super(message); Object.setPrototypeOf(this, MyError.prototype) }
}
const myFunction = () => { throw new MyError('some reason');
}
try { myFunction();
} catch (error) { if (error instanceof MyError) { // Handle MyError.... }
}