Node.js util.inherits Method

The util.inherits() method basically inherits the methods from one construct to another. This prototype will be set to a new object to that from the superConstructor.

By doing this, we can mainly add some validations to the top of Object.setPrototypeOf(constructor.prototype, superConstructor.prototype).

Syntax

util.inherits(constructor, superConstructor)

Parameters

The parameters are described below -

• constructor − This is a function type input that holds the prototype for constructor the user wants to be inherited.
• superConstructor − This is the function that will be used for adding and validating the input validations.

Example 1

Create a file "inherits.js" and copy the following code snippet. After creating the file, use the command "node inherits.js" to run this code.

 Live Demo

// util.inherit() example

// Importing the util module
const util = require('util');
const EventEmitter = require('events');

// Defining the constructor below
function Stream() {
   EventEmitter.call(this);
}

// Inheriting the stream constructor
util.inherits(Stream, EventEmitter);

// Creating the prototype for the constructor with some data
   Stream.prototype.write = function(data) {
   this.emit('data', data);
};

// Creating a new stream constructor
const stream = new Stream();

// Checking if stream is instanceOf EventEmitter
console.log(stream instanceof EventEmitter); // true
console.log(Stream.super_ === EventEmitter); // true

// Printing the data
stream.on('data', (data) => {
   console.log(`Data Received: "${data}"`);
});
// Passing the data in stream
stream.write('Its working... Created the constructor prototype!');

Output

C:\home
ode>> node inherits.js
true
true
Dta Received: "It's working... Created the constructor prototype!"

Example 2

Let’s have a look at one more example

 Live Demo

// util.inherits() example

// Importing the util & events module
const util = require('util');
const { inspect } = require('util');
const emitEvent = require('events');

// Definging the class to emit stream data
class streamData extends emitEvent {
write(stream_data) {
   // This will emit the data stream
   this.emit('stream_data', stream_data);
   }
}

// Creating a new instance of the stream
const manageStream = new streamData('default');
console.log("1.", inspect(manageStream, false, 0, true))
console.log("2.", streamData)

manageStream.on('stream_data', (stream_data) => {
   // Prints the write statement after streaming
   console.log("3.", `Data Stream Received: "${stream_data}"`);
});

// Write on console
manageStream.write('Inheriting the constructor & checking from superConstructor');

Output

C:\home
ode>> node inherits.js
1. streamData {
   _events: [Object: null prototype] {},
   _eventsCount: 0,
   _maxListeners: undefined,
   [Symbol(kCapture)]: false
}
2. [class streamData extends EventEmitter]
3. Data Stream Received: "Inheriting the constructor & checking from superConstructor"