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Been waiting for promises: Unhandled rejections now emit a process warning after the first tick. I'm not sure how useful the warning is though. Now using node

by STRiDEX 10y ago

Been waiting for promises: Unhandled rejections now emit a process warning after the first tick. I'm not sure how useful the warning is though. Now using node v6.6.0 (npm v3.10.3) $ node > Promise.reject() Promise { <rejected> undefined } > (node:85928) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): undefined

danneu 10y ago
This will save a lot of time across the Node ecosystem. Forgetting to handle rejection is probably the most common error I see when people post Promise snippets in #node.js. Silent failure is so deadly. "Why do my requests hang?"
- jamesrom 10y ago
  Sometimes you just want an error to bubble up and be caught above. There's absolutely no reason to catch every rejection in the scope where the promise was created.
  - deleted 10y ago
    [deleted]
  - danneu 10y ago
    Yeah, looks like it just checks on nextTick, so it only warns when you don't attach a handler synchronously. Versus warning only if it's unreachable (like on garbage collection). Though it does emit another message when rejection is handled asynchronously. > var p = new Promise((_, reject) => reject('lol')) \ setTimeout(() => p.catch(() => console.log('handled')), 0) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 5): lol PromiseRejectionHandledWarning: Rejection handled asynchronously (rejection id: 5) Consolation prize? Fortunately, most of the run of the mill promises I can think of off the top of my head get rejection handlers attached synchronously, like in upstream middleware. I might be drawing a blank, though.
tlrobinson 10y ago
It will at least print the rejection value coerced to a string ("undefined" in your example), but line numbers would be nice.
Noseshine 10y ago
What will it give you what 'unhandledRejection' [0] doesn't? I don't mind that it also emits a warning, but AFAIK you could already get that information by subscribing to this more specific event? [0] https://nodejs.org/dist/latest-v6.x/docs/api/process.html#process_event_unhandledrejection https://nodejs.org/dist/latest-v6.x/docs/api/process.html#pr...
- _greim_ 10y ago
  It will hopefully remind you that you forgot to register that event.

by STRiDEX 10y ago

danneu 10y ago

This will save a lot of time across the Node ecosystem. Forgetting to handle rejection is probably the most common error I see when people post Promise snippets in #node.js. Silent failure is so deadly. "Why do my requests hang?"

jamesrom 10y ago
Sometimes you just want an error to bubble up and be caught above. There's absolutely no reason to catch every rejection in the scope where the promise was created.
- deleted 10y ago
  [deleted]
- danneu 10y ago
  Yeah, looks like it just checks on nextTick, so it only warns when you don't attach a handler synchronously. Versus warning only if it's unreachable (like on garbage collection). Though it does emit another message when rejection is handled asynchronously. > var p = new Promise((_, reject) => reject('lol')) \ setTimeout(() => p.catch(() => console.log('handled')), 0) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 5): lol PromiseRejectionHandledWarning: Rejection handled asynchronously (rejection id: 5) Consolation prize? Fortunately, most of the run of the mill promises I can think of off the top of my head get rejection handlers attached synchronously, like in upstream middleware. I might be drawing a blank, though.

tlrobinson 10y ago

It will at least print the rejection value coerced to a string ("undefined" in your example), but line numbers would be nice.

Noseshine 10y ago

What will it give you what 'unhandledRejection' [0] doesn't? I don't mind that it also emits a warning, but AFAIK you could already get that information by subscribing to this more specific event? [0] https://nodejs.org/dist/latest-v6.x/docs/api/process.html#process_event_unhandledrejection https://nodejs.org/dist/latest-v6.x/docs/api/process.html#pr...

_greim_ 10y ago
It will hopefully remind you that you forgot to register that event.