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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Can't narrow error type in catch clause","articleBody":"``` ts\n\ntry {\n    ...\n}\ncatch (ex) { // Adding an annotation here gives ERROR TS1196: Catch clause variable cannot have a type annotation\n    if (ex instanceof FooError) {\n        ex; // ex is of type any\n        ex.message; // OK\n        ex.iDontExist; // typechecks OK, but doesn't exist\n    }\n    else if (isBarError(ex)) {\n        ex; // ex is of type any\n        ex.foo(); // typechecks OK, but runtime error\n    }\n    else {\n        ...\n    }\n}\n```\n\nI guess this is expected behaviour not a bug. But I was not previously aware that the catch clasue variable cannot be annotated. Due to #1426, this means we can't narrow `ex` inside the catch clause, so all the cases dealing with specific error types get no type checking (since `ex` remains as `any`).\n","author":{"url":"https://github.com/yortus","@type":"Person","name":"yortus"},"datePublished":"2016-05-19T00:43:12.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":24},"url":"https://github.com/8677/TypeScript/issues/8677"}