Node.js Process uncaughtException Event

The ‘uncaughtException’ is an event of class Process within the process module which is emitted when an uncaught JavaScript exception bubbles all the way back to the event loop.

Syntax:

Event: 'uncaughtException'

Parameters: This event does not accept any argument as a parameter.

Return Value: This event returns nothing but a callback function for further operation.

Example 1: 

index.js

// Node.js program to demonstrate the
// Process 'uncaughtException' Event

// Importing the modules
const process = require('process');
var fs = require('fs');

// Independent Block which will execute
setTimeout(() => {
   console.log('\n')
   console.log('Greetings from GeeksforGeeks');
}, 1000);

// Event 'uncaughtException'
process.on('uncaughtException', (error, source) => {
   fs.writeSync(process.stderr.fd, error, source);
});

// Throwing an exception
nonexistentFunc();

console.log('This Block of code will not run');

Run the index.js file using the following command:

node index.js

Output:

ReferenceError: nonexistentFunc is not defined

Greetings from GeeksforGeeks

Example 2:

index.js

// Node.js program to demonstrate the
// Process 'uncaughtException' Event

// Importing the modules
const process = require('process');
var fs = require('fs');

// Event 'uncaughtException'
process.on('uncaughtException', (error) => {
   fs.writeSync(process.stderr.fd, error);
});

// Throwing our Error
throw new Error('Ran out of coffee')

Run the index.js file using the following command:

node index.js

Output:

Error: Ran out of coffee

Reference: https://nodejs.org/dist/latest-v16.x/docs/api/process.html#process_event_uncaughtexception