Express.js res.download() Function

The res.download() function transfers the file at the path as an 'attachment'. Typically, browsers will prompt the user to download.

Syntax:

res.download(path [, filename] [, options] [, fn])

Parameters: The filename is the name of the file which is to be downloaded as an attachment and fn is a callback function. 

Return Value: It does not return anything. 

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

The res.download() function in Express.js allows you to download files from the server.

Example 1: Filename: index.js 

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

app.get('/', function (req, res) {
    res.download('Hello.txt');
});

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

Place any file in the root directory of the project which can be downloaded, like here we have used Hello.txt. 

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:

Server listening on PORT 3000

Open your browser and go to http://localhost:3000/, now you can see the "Hello.txt" file being downloaded on your screen.

Example 2: Filename: index.js 

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

app.get('/', function (req, res) {
    res.download('Unknown_file.txt', function (error) {
        console.log("Error : ", error)
    });
});

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:

Browser Output:

Open your browser and go to http://localhost:3000/, then you will see the following output on your console:

Error :  [Error: ENOENT: no such file or directory, 
      stat 'C:\\Users\\Unknown_file.txt'] {
      errno: -4058,
      code: 'ENOENT',
      syscall: 'stat',
      path: 'C:\\Users\\Unknown_file.txt',
      expose: false,
      statusCode: 404,
      status: 404
}

Reference: https://expressjs.com/en/4x/api.html#res.download