Node.js Process message Event

Last Updated : 07 Aug, 2021

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

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