Express.js res.sendFile() Function

The res.sendFile() function basically transfers the file at the given path and it sets the Content-Type response HTTP header field based on the filename extension. 
Syntax:

res.sendFile(path [, options] [, fn])

Parameter: The path parameter describes the path and the options parameter contains various properties like maxAge, root, etc and fn is the callback function.
Returns: It returns an Object.
Installation of express module:

• You can visit the link to Install 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 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

Example 1: Filename: index.js

javascript

var express = require('express');
var app = express();
var path = require('path');
var PORT = 3000;

// Without middleware
app.get('/', function(req, res){
    var options = {
        root: path.join(__dirname)
    };

    var fileName = 'Hello.txt';
    res.sendFile(fileName, options, function (err) {
        if (err) {
            next(err);
        } else {
            console.log('Sent:', fileName);
        }
    });
});

app.listen(PORT, function(err){
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);
});

Now, create a .txt file like here we have created Hello.txt in the root directory of project with the following text:  

Greetings from GeeksforGeeks

Steps to run the program:

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

npm install express

• Run index.js file using below command: 

node index.js

Output:

Server listening on PORT 3000

• Now open browser and go to http://localhost:3000/, now check your console and you will see the following output: 

Server listening on PORT 3000
Sent: Hello.txt

• And on screen you will see the following output: 

Greetings from GeeksforGeeks

Example 2: Filename: index.js

javascript

var express = require('express');
const path = require('path');
var app = express();
var PORT = 3000;

// With middleware
app.use('/', function(req, res, next){

    var options = {
        root: path.join(__dirname)
    };

    var fileName = 'GeeksforGeeks.txt';
    res.sendFile(fileName, options, function (err) {
        if (err) {
            next(err);
        } else {
            console.log('Sent:', fileName);
            next();
        }
    });
});

app.get('/', function(req, res){
    console.log("File Sent")
    res.send();
});

app.listen(PORT, function(err){
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);
});

Make sure you create a .txt file like here we have created GeeksforGeeks.txt in the root directory of project with the following text:  

Welcome from GeeksforGeeks

Run index.js file using below command:  

node index.js

Now open the browser and go to http://localhost:3000/, now check your console and you will see the following output:  

Server listening on PORT 3000
Sent: GeeksforGeeks.txt
File Sent

And you will see the following output on your browser screen:  

Welcome from GeeksforGeeks

Reference: https://expressjs.com/en/5x/api.html#res.sendFile