CODEWITHSUNDEEP
node.jstypescriptexceptiondeno
Storm 7953
Storm 7953

Reputation: 149

Deno: How to handle exceptions

In nodejs, we can handle exceptions like this:

process.on('uncaughtException', (err, origin) => {
  fs.writeSync(
    process.stderr.fd,
    `Caught exception: ${err}\n` +
    `Exception origin: ${origin}`
  );
});

setTimeout(() => {
  console.log('This will still run.');
}, 500);

// Intentionally cause an exception, but don't catch it.
nonexistentFunc();
console.log('This will not run.');

What is the alternative for deno? I know there is window.onunload, but it doesn't handle errors

Upvotes: 5

Views: 3498

Answers (1)

Steven Guerrero
Steven Guerrero

Reputation: 1056

It's a design choice (a central one actually) for Deno to always die on uncaught exceptions. You can not place a global handler for your errors, since sometimes your exceptions might be non recoverable and may cause side effects that change the overall state of your application, in summary, unhandled exception handlers mean problems. Global handling of exceptions it's being discouraged by NodeJS as of now so please don't rely on this kind of code in the future in that platform either.

That being said, how to handle rejections? try/catch/finally for sync code. .then/.catch/.finally for async code.

EDIT: An interesting resource you can use is the unhandledRejection event, it's an event meant to be used to realize a cleanup of sorts, meaning to close open connections, free up resources, close files, etc. This won't stop the exception from terminating the program, but will give you space to prevent secondary effects on the program termination.

https://developer.mozilla.org/en-US/docs/Web/API/Window/unhandledrejection_event

Upvotes: 5

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