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75 lines
2.4 KiB
Markdown
75 lines
2.4 KiB
Markdown
# signal-exit
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When you want to fire an event no matter how a process exits:
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- reaching the end of execution.
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- explicitly having `process.exit(code)` called.
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- having `process.kill(pid, sig)` called.
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- receiving a fatal signal from outside the process
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Use `signal-exit`.
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```js
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// Hybrid module, either works
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import { onExit } from 'signal-exit'
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// or:
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// const { onExit } = require('signal-exit')
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onExit((code, signal) => {
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console.log('process exited!', code, signal)
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})
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```
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## API
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`remove = onExit((code, signal) => {}, options)`
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The return value of the function is a function that will remove
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the handler.
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Note that the function _only_ fires for signals if the signal
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would cause the process to exit. That is, there are no other
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listeners, and it is a fatal signal.
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If the global `process` object is not suitable for this purpose
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(ie, it's unset, or doesn't have an `emit` method, etc.) then the
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`onExit` function is a no-op that returns a no-op `remove` method.
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### Options
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- `alwaysLast`: Run this handler after any other signal or exit
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handlers. This causes `process.emit` to be monkeypatched.
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### Capturing Signal Exits
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If the handler returns an exact boolean `true`, and the exit is a
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due to signal, then the signal will be considered handled, and
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will _not_ trigger a synthetic `process.kill(process.pid,
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signal)` after firing the `onExit` handlers.
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In this case, it your responsibility as the caller to exit with a
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signal (for example, by calling `process.kill()`) if you wish to
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preserve the same exit status that would otherwise have occurred.
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If you do not, then the process will likely exit gracefully with
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status 0 at some point, assuming that no other terminating signal
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or other exit trigger occurs.
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Prior to calling handlers, the `onExit` machinery is unloaded, so
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any subsequent exits or signals will not be handled, even if the
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signal is captured and the exit is thus prevented.
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Note that numeric code exits may indicate that the process is
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already committed to exiting, for example due to a fatal
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exception or unhandled promise rejection, and so there is no way to
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prevent it safely.
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### Browser Fallback
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The `'signal-exit/browser'` module is the same fallback shim that
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just doesn't do anything, but presents the same function
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interface.
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Patches welcome to add something that hooks onto
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`window.onbeforeunload` or similar, but it might just not be a
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thing that makes sense there.
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