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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Default Unhandled Rejection Detection Behavior","articleBody":"With https://github.com/iojs/io.js/pull/758/ (hopefully) soon landing to address https://github.com/iojs/io.js/issues/256 we will soon have unhandled promise rejections reported to the process via a `process.on(\"unhandledRejection\"` event. \n\nOne issue that was deliberately deferred from that issue and PR is what the default behaviour of an unhandled promise rejection detected be.\n\nJust to be clear - this is about the default behaviour of a rejected promise with no `catch` handler (or `then` handler with a function second argument) attached.\n## **The different approaches**\n- Logging the rejection to the console.\n- Throwing an error for `process.on(\"uncaughtException\"` to deal with.\n- Causing the process to exit.\n- Do nothing by default.\n\nThere are several good arguments for each approach. I'll write down the arguments I'm aware of and will edit arguments as people make them in comments.\n### Logging\n- No silent failure by default.\n- Does not break any existing code - no \"surprises\". (See comment by @vkurchatkin on this)\n- Been a default in several userland libraries like bluebird and users have been very satisfied with it.\n### Throwing an error\n- A promise rejection is the asynchronous version of a thrown exception.\n- Does not ignore logical errors or leave the app in an inconsistent state. \n- False positives are extremely rare - and code causing them can arguably easily be refactored to not cause them by not attaching error handlers too late.\n### Process Exit\n- Differentiation between uncaught exceptions and promise rejections might be useful.\n### Do nothing\n- Reliable promise rejection detection is non-deciable, it's possible to report an unhandled rejection that actually is handled at a later point if the catch handler is attached at a very late time. \n- Does not break any existing workflows for anyone. No backwards compatibility issues for native promise users at all.\n- Does not make any assumptions on how people use native promises.\n\n---\n\nWhat do people think the default behaviour should be?\n","author":{"url":"https://github.com/benjamingr","@type":"Person","name":"benjamingr"},"datePublished":"2015-02-13T11:31:38.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":135},"url":"https://github.com/830/node/issues/830"}