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Express.js Mount Event

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The mount event is fired on a sub-app when it is mounted on a parent app and the parent app is basically passed to the callback function. 

Syntax:

app.on('mount', callback(parent))

Parameter: It is an event named ‘mount’, and the callback function is called when this event is called. 

Return Value: Since it’s an event so it doesn’t have any return value. 

Installation of the express module:

You can visit the link to Install the express module. You can install this package by using this command.

npm install express

After installing the express module, you can check your express version in the command prompt using the command.

npm version express

After that, you can just create a folder and add a file, for example, index.js. To run this file you need to run the following command.

node index.js

Project Structure:

Example 1: Filename: index.js 

javascript




const express = require('express');
const app = express(); // The main app
const admin = express();
const PORT = 3000;
 
admin.on('mount', function (parent) {
    console.log('Admin Mounted');
});
 
admin.get('/', function (req, res) {
    res.send('Admin Homepage');
});
 
app.use('/admin', admin);
 
app.listen(PORT, function (err) {
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);
});


Steps to run the program:

Make sure you have installed the express module using the following command:

npm install express

Run the index.js file using the below command:

node index.js

Output:

Console Output:

Admin Mounted
Server listening on PORT 3000

Browser Output:

Now open your browser and go to http://localhost:3000/admin, now you can see the following output on your screen:

Admin Homepage

Example 2: Filename: index.js 

javascript




const express = require('express');
const app = express(); // The main app
const student = express();
const teacher = express();
const PORT = 3000;
 
// Multiple mounting
teacher.on('mount', function (parent) {
    console.log('Teacher Mounted');
});
 
student.on('mount', function (parent) {
    console.log('Student Mounted');
});
 
app.use('/student', student);
app.use('/teacher', teacher);
 
app.listen(PORT, function (err) {
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);
});


Steps to run the program:

Run the index.js file using the below command:

node index.js

Output: Now open your browser and make a GET request to http://localhost:3000, now you can see the following output on your console:

Student Mounted
Teacher Mounted
Server listening on PORT 3000

Reference: https://expressjs.com/en/4x/api.html#app.onmount


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Last Updated : 20 Mar, 2023
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