res.download for file downloads in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to send a file named 'report.pdf' for download using Express.

Express

app.get('/download', (req, res) => {
  res.[1]('report.pdf');
});

Drag options to blanks, or click blank then click option'

Adownload

Bredirect

Csend

DsendFile

Attempts:

3 left

💡 Hint

Common Mistakes

Using res.sendFile instead of res.download

Using res.redirect which is for URL redirection

The res.download() method sends a file as an HTTP attachment, prompting the user to download it.

2fill in blank

medium

Complete the code to specify a custom filename 'user_report.pdf' for the downloaded file.

Express

app.get('/download', (req, res) => {
  res.download('report.pdf', [1]);
});

Drag options to blanks, or click blank then click option'

A'download.pdf'

B'user_report.pdf'

C'file.pdf'

D'report_download.pdf'

Attempts:

3 left

💡 Hint

Common Mistakes

Using the original file path instead of a filename

Omitting quotes around the filename

The second argument to res.download() sets the filename the user sees when downloading.

3fill in blank

hard

Fix the error in the code to handle errors during file download.

Express

app.get('/download', (req, res) => {
  res.download('report.pdf', ([1]) => {
    if (err) {
      res.status(500).send('Error downloading file');
    }
  });
});

Drag options to blanks, or click blank then click option'

Aexception

Berror

Ce

Derr

Attempts:

3 left

💡 Hint

Common Mistakes

Using a parameter name different from the one checked inside the callback

Not including the error parameter at all

The callback receives an error object named err by convention to check if the download failed.

4fill in blank

hard

Fill both blanks to send 'report.pdf' for download and handle errors by sending a 404 status.

Express

app.get('/download', (req, res) => {
  res.[1]('report.pdf', ([2]) => {
    if ([2]) {
      res.status(404).send('File not found');
    }
  });
});

Drag options to blanks, or click blank then click option'

Adownload

Berr

CsendFile

Derror

Attempts:

3 left

💡 Hint

Common Mistakes

Using res.sendFile instead of res.download

Using a wrong parameter name for the error

res.download sends the file, and the callback receives err to check for errors.

5fill in blank

hard

Fill all three blanks to send 'report.pdf' for download with a custom filename 'summary.pdf' and handle errors by logging them.

Express

app.get('/download', (req, res) => {
  res.[1]('report.pdf', [2], ([3]) => {
    if ([3]) {
      console.error('Download error:', [3]);
      res.status(500).send('Download failed');
    }
  });
});

Drag options to blanks, or click blank then click option'

Adownload

B'summary.pdf'

Cerr

DsendFile

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the custom filename argument

Using wrong parameter names in the callback

Using res.sendFile instead of res.download

The res.download method takes the file path, the custom filename, and a callback with an error parameter.

Practice

1. What does res.download() do in an Express app?

easy

A. Uploads a file from the user to the server

B. Sends a file to the user for download

C. Deletes a file on the server

D. Reads a file and logs its content

Solution

1. Step 1: Understand the purpose of res.download

   res.download() is used to send files to users so they can download them easily.

2. Step 2: Compare with other file operations

   Uploading, deleting, or reading files are different operations and not what res.download() does.

3. Final Answer:

   Sends a file to the user for download -> Option B

4. Quick Check:

   res.download() = Sends file [OK]

Hint: Remember: download means sending file to user [OK]

Common Mistakes:

• Confusing download with upload
• Thinking it deletes files
• Assuming it reads file content

2. Which is the correct syntax to send a file named report.pdf for download using res.download?

easy

A. res.download('report.pdf')

B. res.download(report.pdf)

C. res.download('report.pdf', 'download')

D. res.download('report.pdf', {filename: 'download.pdf'})

Solution

1. Step 1: Check the basic usage of res.download

   The first argument is the file path as a string, so res.download('report.pdf') is correct.

2. Step 2: Analyze other options

   res.download(report.pdf) misses quotes making it invalid syntax. res.download('report.pdf', 'download') adds a second argument incorrectly as a string. res.download('report.pdf', {filename: 'download.pdf'}) uses an object which is not valid for filename.

3. Final Answer:

   res.download('report.pdf') -> Option A

4. Quick Check:

   File path string only = res.download('report.pdf') [OK]

Hint: File path must be a string in quotes [OK]

Common Mistakes:

• Omitting quotes around filename
• Passing wrong argument types
• Using object instead of string for filename

3. What will happen when this code runs?

app.get('/file', (req, res) => {
  res.download('files/data.txt', 'info.txt');
});

medium

A. The file 'files/data.txt' is sent and saved as 'info.txt' by the user

B. The file 'info.txt' is sent from the server

C. An error occurs because the second argument is invalid

D. The file 'data.txt' is sent without renaming

Solution

1. Step 1: Understand res.download parameters

   The first argument is the path on the server, the second is the filename for the user.

2. Step 2: Apply to given code

   The server sends 'files/data.txt' but the user will see it saved as 'info.txt'.

3. Final Answer:

   The file 'files/data.txt' is sent and saved as 'info.txt' by the user -> Option A

4. Quick Check:

   res.download(path, filename) renames file [OK]

Hint: Second argument renames file for user [OK]

Common Mistakes:

• Thinking second argument is server file path
• Assuming no renaming happens
• Believing second argument causes error

4. Identify the error in this code snippet:

app.get('/download', (req, res) => {
  res.download();
});

medium

A. res.download requires a callback as first argument

B. res.download cannot be used inside app.get

C. No error, code works fine

D. Missing file path argument in res.download

Solution

1. Step 1: Check res.download required arguments

   res.download() requires at least the file path as the first argument.

2. Step 2: Analyze given code

   The code calls res.download() with no arguments, causing an error.

3. Final Answer:

   Missing file path argument in res.download -> Option D

4. Quick Check:

   res.download needs file path [OK]

Hint: Always provide file path to res.download [OK]

Common Mistakes:

• Calling res.download without arguments
• Thinking res.download needs callback first
• Assuming no error if arguments missing

5. You want to send a file report.pdf for download but also handle errors if the file is missing. Which code correctly does this?

hard

A. res.download('report.pdf', (err) => { if (err) throw err; });

B. res.download('report.pdf').catch(() => res.status(404).send('File not found'));

C. res.download('report.pdf', err => { if (err) res.status(404).send('File not found'); });

D. res.download('report.pdf', 'report.pdf', err => { if (err) res.send('Error'); });

Solution

1. Step 1: Understand error handling in res.download

   res.download accepts an optional callback as the last argument to handle errors.

2. Step 2: Check each option

   res.download('report.pdf', err => { if (err) res.status(404).send('File not found'); }); uses the callback correctly to send 404 if error occurs. res.download('report.pdf').catch(() => res.status(404).send('File not found')); wrongly uses .catch which is not supported. res.download('report.pdf', 'report.pdf', err => { if (err) res.send('Error'); }); has an extra filename argument which is unnecessary here. res.download('report.pdf', (err) => { if (err) throw err; }); throws error instead of handling gracefully.

3. Final Answer:

   res.download('report.pdf', err => { if (err) res.status(404).send('File not found'); }); -> Option C

4. Quick Check:

   Use callback to handle errors in res.download [OK]

Hint: Use callback function to catch errors in res.download [OK]

Common Mistakes:

• Using promises or .catch with res.download
• Not handling errors at all
• Passing wrong number of arguments