Express.js res.download() Function

Last Updated : 07 Jul, 2020

The res.download() function transfers the file at 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 attachment and fn is a callback function.

Return Value: It does not return anything.

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

var express = require('express');
var app = express();
var 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 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 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
```
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

var express = require('express');
var app = express();
var 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);
});

Run index.js file using below command:

node index.js

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

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