From 72d29e6afdedab3440f3f028c59c018fe35f501e Mon Sep 17 00:00:00 2001 From: James M Snell Date: Wed, 17 Feb 2016 11:10:46 -0800 Subject: [PATCH] doc: improve unhandledException doc copy Rework the doc a bit to tighten it up, including removing the use of `you` --- doc/api/process.markdown | 35 ++++++++++++++++++----------------- 1 file changed, 18 insertions(+), 17 deletions(-) diff --git a/doc/api/process.markdown b/doc/api/process.markdown index ca2971328025c5..2f20f730d36e66 100644 --- a/doc/api/process.markdown +++ b/doc/api/process.markdown @@ -91,11 +91,11 @@ indefinitely) or upon process exit (more convenient for scripts). ## Event: 'uncaughtException' -Emitted when an exception bubbles all the way back to the event loop. If a -listener is added for this exception, the default action (which is to print -a stack trace and exit) will not occur. +The `'uncaughtException'` event is emitted when an exception bubbles all the +way back to the event loop. By default, Node.js handles such exceptions by printing the stack trace to stderr and exiting. Adding a handler for the +`'uncaughtException'` event overrides this default behavior. -Example of listening for `'uncaughtException'`: +For example: ```js process.on('uncaughtException', (err) => { @@ -111,26 +111,27 @@ nonexistentFunc(); console.log('This will not run.'); ``` -Note that `'uncaughtException'` is a very crude mechanism for exception -handling. +### Warning: Using `'uncaughtException'` correctly -Do *not* use it as the Node.js equivalent of `On Error Resume Next`. An -unhandled exception means your application - and by extension Node.js itself - -is in an undefined state. Blindly resuming means *anything* could happen. +Note that `'uncaughtException'` is a crude mechanism for exception handling +intended to be used only as a last resort. The event *should not* be used as +an equivalent to `On Error Resume Next`. Unhandled exceptions inherently mean +that an application is in an undefined state. Attempting to resume application +code without properly recovering from the exception can cause additional +unforeseen and unpredictable issues. Exceptions thrown from within the event handler will not be caught. Instead the process will exit with a non zero exit code and the stack trace will be printed. This is to avoid infinite recursion. -Think of resuming as pulling the power cord when you are upgrading your system. -Nine out of ten times nothing happens - but the 10th time, your system is bust. +Attempting to resume normally after an uncaught exception can be similar to +pulling out of the power cord when upgrading a computer -- nine out of ten +times nothing happens - but the 10th time, the system becomes corrupted. -`'uncaughtException'` should be used to perform synchronous cleanup before -shutting down the process. It is not safe to resume normal operation after -`'uncaughtException'`. If you do use it, restart your application after every -unhandled exception! - -You have been warned. +The correct use of `'uncaughtException'` is to perform synchronous cleanup +of allocated resources (e.g. file descriptors, handles, etc) before shutting +down the process. It is not safe to resume normal operation after +`'uncaughtException'`. ## Event: 'unhandledRejection'