Events and Event Emitter in nodejs

 

 

 

Events and Event Emitter in nodejs

This blog we have seen mongodb basic and how is it work with installation and after installation, we have already seen mongodb basic, CRUD operation, connect mongodb with nodejs, read, update, delete, POST, GET API etc. we should not face any problem while making Database, collection(table) and using the data in nodejs even whenever we will make API. Read data from mongodb in nodejs

• # What is Mongoose
• # Install Mongoose
  
• # What is Events and Event Emitter
  
• # Make an event and call it
  

 

Now in this blog  we will use mongoose. There is an npm package to connect nodes to mongodb. Mongoose is a MongoDB object modeling tool designed to work in an asynchronous environment. They created mongoose by improving mongodb, with the help of which you can create schemas and models of mongoose's movements.

Suppose that there are 4 fields in our database (like name, brand, price, category) and the user wants to add a 5th field also (like color) but we want to add only 4 fields, for this we create schemas.

Here you can also define TYPE in schemas like price type is numeric but if any user wants to use quotes (" " ' ') then we can stop the user for this.

in sort we can apply validation in mongoose but we can't in directly mongodb.

 

 

 What is MongoDB

 

MongoDB is a popular open-source NoSQL (non-relational) database management system. NoSQL means no structure like it is look like an object while in SQL it is a structure query language like SELECT CustomerName, City FROM Customers; (The SELECT statement is used to select data from a database.) But NoSQL database is useless...NOT completely because of whenever we want add extra column in database then it is possible through NoSQL MongoDB.   

 

MongoDB installation - CLICK HERE

MongoDB Basic Command - CLICK HERE

About MongoDB vs SQL - CLICK HERE

CRUD in MongoDB - CLICK HERE

 

 

Object Like - 

 

 

{
  "_id": {
    "$oid": "659ad46e0382148123c82841"
  },
  "name": "moto G60",
  "brand": "motorola",
  "price": 16500,
  "category": "mobile"
}

 

 

MongoDB is a type of database that helps store and manage large amounts of data in a flexible and scalable way. Unlike SQL, MongoDB doesn't require a fixed structure for the data, allowing you to store information in a more versatile format.

• MongoDB is a NoSQL database.
• The data stored in a collection
• Collection don't have row and columns
• Data is stored in the form of object.

Install Mongoose

For this you need to copy this (npm i mongoose) and paste it in project's terminal.

https://www.npmjs.com/package/mongoose

 

 

 

 

 

What is Events and Event Emitter

 

In nodejs, an event is an action or occurrence that can be observed and responded to . Node.js provides the event emitter pattern as a core module to handle events. The Event emitter is an implementation of the observer pattern allowing objects (event emitter) to emit the named events that cause function objects (listeners) to be called.

 

OR

 

if i will use button in HTML and add the onClick event and whenever we click on button and generate the function and get a signal that please call the function and execute the code.

and the event is that which observes the singal received from the event and works on that pattern.

Basic Usage:

To use the Event Emitter, you first create an instance of Event Emitter.

You can then use the .on(eventName, listener) method to attach a listener function to a specific event.

The .emit(eventName, ...args) method is used to emit (trigger) an event, and any attached listeners for that event are called.

 

 

Q) How can we make a button in Node.js ?

 Ans - Through API and use Event Emitter

 

 

Make an event and call it

 

First we will make a API and import express and EventEmitter (EventEmitter is inbuilt module in nodejs) so don't need to install in nodejs.

const express = require('express')
const EventEmitter = require('events');
const app = express()


app.get("/", (req, resp) => {
    resp.send("Done")
    console.log("API called")
})

app.listen(8000)

 

 

 

 

Now we will see when we create so many API then we will check how many hit on particular API.

 

app.get("/", (req, resp) => {
    resp.send("Home page API")
    console.log("Home page API called")
})


app.get("/search", (req, resp) => {
    resp.send("Search API")
    console.log("Search API called")
})



app.get("/update", (req, resp) => {
    resp.send("update page API")
    console.log("update API called")
})

 

 

 Now we make a function that means it will keep updating the count of every hit we get on our API in the database.

const express = require("express");
const EventEmitter = require("events");
const app = express();

const event = new EventEmitter();
//this is object

let count = 0;

event.on("countAPI", () => {
  count++;
  console.log("Event called", count);
});

//first is the event name - countAPI
//second is the callback function



app.get("/", (req, resp) => {
  resp.send("Home page API");
  event.emit("countAPI"); 
});

app.get("/search", (req, resp) => {
  resp.send("Search API");
  event.emit("countAPI"); 
});
 
app.get("/update", (req, resp) => {
  resp.send("update page API");
  event.emit("countAPI");
});

app.listen(8000);

 

 

 

 

 

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