Node.js Process message Event

The ‘message’ is an event of class Process within the process module which is emitted whenever a message sent by a parent process using childprocess.send() is received by the child process.

Syntax:

Event: 'message'

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:

The filename is index.js

Javascript

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

// Importing process module
const cp = require('child_process');

// Initiating child process
const process = cp.fork(`${__dirname}/sub.js`);

// Causes the child to print:
// CHILD got message: { hello: 'world' }
process.send({ hello: 'world' });

Here the file name is sub.js

Javascript

// Importing process module
const process = require('process');

// Message Event
process.on('message', (m) => {
    console.log('CHILD got message:', m);
    process.exit(0)
});

Run the index.js file using the following command:

node index.js

Output:

CHILD got message: { hello: 'world' }

Example 2:

The filename is index.js

Javascript

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

// Importing process module
const cp = require('child_process');

// Initiating child process
const process = cp.fork(`${__dirname}/sub.js`);

// Message Event
process.on('message', (m) => {
    console.log('PARENT got message:', m);
});

// Causes the child to print:
// CHILD got message: { hello: 'world' }
process.send({ hello: 'world' });

Here the filename is sub.js

Javascript

// Importing process module
const process = require('process');

// Message Event
process.on('message', (m) => {
    console.log('CHILD got message:', m);
    process.exit(0)
});

// Causes the parent to print:
// PARENT got message: { foo: 'bar', baz: null }
process.send({ foo: 'bar', baz: NaN });

Run the index.js file using the following command:

node index.js

Output:

CHILD got message: { hello: 'world' }
PARENT got message: { foo: 'bar', baz: null }

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