Node.js util.inherits() Method

The “util” module provides ‘utility’ functions that are used for debugging purposes. For accessing those functions we need to call them (by ‘require(‘util’)‘).

The util.inherits() (Added in v0.3.0) method is an inbuilt application programming interface of the util module in which the constructor inherits the prototype methods from one to another and the prototype of that constructor is set to a new object which is created from superConstructor. It is mostly used for adding or inheriting some input validation on top of Object.setPrototypeOf(constructor.prototype, superConstructor.prototype). And superConstructor can be accessed through the constructor.super_property for additional convenience. Its (i.e, util.inherits()) usage is not much encouraged instead use of ES6 class and extends keywords is recommended in order to get language level inheritance support.

Syntax:

const util = require('util');
util.inherits(constructor, superConstructor)

Parameters: This function accepts two parameters as mentioned above and described below:

• constructor <Function>:  It is any <function> that the user wants to be inherited from the class.

• superConstructor <Function>: It is any <function> which is mostly used for adding or inheriting some input validation.

Return Value <undefined>: It returns undefined value.

Example 1: Filename: index.js








// Node.js program to demonstrate the  // util.inherits() method     // Using require to access util module  const util = require('util');  const emitEvent = require('events');    // MyStream function calling EventEmitter function streamData() {   emitEvent.call(this); }    // Trying to print value console.log("1.> Returning util.inherits():",  util.inherits(streamData, emitEvent));  // Returns undefined    // Inheriting library via constructor console.log("2.>", streamData); // Whole library of the constructor    console.log("3.>", emitEvent); // Inheriting from EventEmitter  util.inherits(streamData, emitEvent);    // Emitting events streamData.prototype.write = function(responseData) {   this.emit('send_data', responseData); };    // Creating new stream by calling function const stream = new streamData('default'); // Printing instance of eventemitter console.log("4.> Instance of EventEmitter",                stream instanceof emitEvent);  // Returns true    // Comparing value and type of an  // instance with eventEmitter console.log("5.> '===' comparison of an "           + "Instance with EventEmitter",  streamData.super_ === emitEvent);  // Returns true    stream.on('send_data', (responseData) => {   console.log("6.>",    `Data Stream Received: "${responseData}"`); });    // Writing on console stream.write('Finally it started!');  // Finally Received the data

Run index.js file using the following command:

node index.js

Output:

1.> Returning util.inherits(): undefined

2.> [Function: streamData]

3.> <ref *1> [Function: EventEmitter] {once: [Function: once], ….., listenerCount: [Function (anonymous)]}

4.> Instance of EventEmitter true

5.> ‘===’ comparison of an Instance with EventEmitter true

6.> Data Stream Received: “Finally it started!”

Example 2: Filename: index.js








// Node.js program to demonstrate the  // util.inherits() method in ES6    // Using require to access util module  const util = require('util'); const { inspect } = require('util'); const emitEvent = require('events');    class streamData extends emitEvent {   write(stream_data) {          // Emitting the data stream     this.emit('stream_data', stream_data);   } }    const manageStream = new streamData('default'); console.log("1.>", inspect(manageStream, false, 0, true)) console.log("2.>", streamData)    // Returns true console.log("3.>", streamData === manageStream)  console.log("4.>", manageStream) manageStream.on('stream_data', (stream_data) => {   // Prints the write statement after streaming   console.log("5.>", `Data Stream Received: "${stream_data}"`); });    // Write on console manageStream.write('Finally it started streaming with ES6');

Run index.js file using the following command:

node index.js

Output:

1.> streamData { _events: [Object: null prototype] {}, ……………………, [Symbol(kCapture)]: false}

2.> [Function: streamData]

3.> false

4.> streamData {_events: [Object: null prototype] {}, ……………………, [Symbol(kCapture)]: false}

5.> Data Stream Received: “Finally it started streaming with ES6”

Reference: https://nodejs.org/api/util.html#util_util_inherits_constructor_superconstructor





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