René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Allow `: { }` / `: any` type annotations on catch variables","articleBody":"It was pointed out in #9999 that `catch` variables never get narrowed because they're of type `any`, and you can't change their type because they're not allowed to have type annotations.\n\nThis leads to pitfalls like\n\n``` ts\ntry {\n  // do something\n} catch(e) {\n  if(e instanceof MyError) {\n    console.log(e.filname); // oops.\n  }\n}\n```\n\nProposal: allow type annotations on catch variables as long as the annotated type is exactly `any` or `{ }` (we can't reasonably make this an implicit any according to `--noImplicitAny` so that behavior would be unchanged). But now \"safer\" developers can write\n\n``` ts\ntry {\n  // do something\n} catch(e: { }) {\n  if(e instanceof MyError) {\n    console.log(e.filname); // error, property not found\n  }\n  console.log(e.filename); // error, forgot to narrow with a guard\n}\n```\n\nAlternatively (or in addition to), we could just let `catch` variables get narrowed despite being `any`, but this would be a fairly odd carve-out.\n","author":{"url":"https://github.com/RyanCavanaugh","@type":"Person","name":"RyanCavanaugh"},"datePublished":"2016-07-28T05:01:18.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/10000/TypeScript/issues/10000"}