Multer middleware setup in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import Multer in an Express app.

Express

const multer = require('[1]');

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

Amulter

Bexpress

Cbody-parser

Dcors

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'express' instead of 'multer' in the require statement.

Forgetting to import multer before using it.

You need to import the 'multer' package to use it as middleware.

2fill in blank

medium

Complete the code to create a Multer instance with default storage.

Express

const upload = multer({ [1] });

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

Afolder: 'uploads/'

Bstorage: 'uploads/'

Cpath: 'uploads/'

Ddest: 'uploads/'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'storage' with a string instead of a storage engine.

Using 'path' or 'folder' which are not valid Multer options.

The 'dest' option tells Multer where to save uploaded files.

3fill in blank

hard

Fix the error in the route to use Multer middleware for single file upload named 'avatar'.

Express

app.post('/profile', upload.[1]('avatar'), (req, res) => {
  res.send('File uploaded');
});

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

Afiles

Barray

Csingle

Dfields

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'files' which is not a Multer method.

Using 'array' or 'fields' when only one file is expected.

The 'single' method handles uploading one file with the given field name.

4fill in blank

hard

Fill both blanks to configure Multer to accept multiple files named 'photos' with a max count of 3.

Express

app.post('/upload', upload.[1]('photos', [2]), (req, res) => {
  res.send('Multiple files uploaded');
});

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

Aarray

B3

C5

Dsingle

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'single' instead of 'array' for multiple files.

Setting max count to a wrong number or missing it.

The 'array' method accepts multiple files with the given field name and max count.

5fill in blank

hard

Fill all three blanks to create a Multer storage engine that saves files with original name in 'uploads/' folder.

Express

const storage = multer.diskStorage({
  destination: function (req, file, cb) {
    cb(null, '[1]');
  },
  filename: function (req, file, cb) {
    cb(null, file.[2]);
  }
});

const upload = multer({ storage: [3] });

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

Auploads/

Boriginalname

Cstorage

Dfilename

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'filename' instead of 'originalname' for the file name.

Passing the wrong variable to Multer storage option.

This sets the destination folder to 'uploads/', uses the original file name, and assigns the storage engine to Multer.

Practice

1. What is the primary purpose of the multer middleware in an Express application?

easy

A. To serve static files like images and CSS

B. To parse JSON data in request bodies

C. To handle file uploads from client requests

D. To manage user sessions and cookies

Solution

1. Step 1: Understand middleware role

   Multer is middleware designed specifically to handle multipart/form-data, which is used for uploading files.

2. Step 2: Compare with other middleware

   Other middleware like body-parser handle JSON, and express.static serves static files, but multer focuses on file uploads.

3. Final Answer:

   To handle file uploads from client requests -> Option C

4. Quick Check:

   Multer = file upload handler [OK]

Hint: Multer is for file uploads, not JSON or sessions [OK]

Common Mistakes:

• Confusing multer with body-parser for JSON parsing
• Thinking multer manages sessions or cookies
• Assuming multer serves static files

2. Which of the following is the correct way to set up multer to accept a single file upload with the field name 'avatar'?

easy

A. const upload = multer().single('avatar');

B. const upload = multer.single('avatar');

C. const upload = multer().array('avatar');

D. const upload = multer().multi('avatar');

Solution

1. Step 1: Correct multer initialization

   Multer must be called as a function to create an instance: multer().

2. Step 2: Use .single() for single file

   To accept one file, use upload.single('fieldname'). Here, 'avatar' is the field name.

3. Final Answer:

   const upload = multer().single('avatar'); -> Option A

4. Quick Check:

   multer() + .single('avatar') = correct setup [OK]

Hint: Always call multer() before .single() or .array() [OK]

Common Mistakes:

• Calling multer.single() without parentheses
• Using .array() instead of .single() for one file
• Using non-existent .multi() method

3. Given this Express route setup with multer:

const multer = require('multer');
const upload = multer({ dest: 'uploads/' });

app.post('/profile', upload.single('photo'), (req, res) => {
  res.send(req.file.path);
});

What will be the response when a user uploads a file named 'pic.jpg' in the 'photo' field?

medium

A. Undefined, because req.file is not set

B. The original filename 'pic.jpg'

C. An error because 'dest' is not a valid option

D. The path where the file is saved, like 'uploads/abc123'

Solution

1. Step 1: Understand multer storage with 'dest'

   Setting 'dest' tells multer to save files to that folder with a generated filename, not the original name.

2. Step 2: Check what req.file.path contains

   req.file.path contains the full path to the saved file, e.g., 'uploads/abc123'.

3. Final Answer:

   The path where the file is saved, like 'uploads/abc123' -> Option D

4. Quick Check:

   dest option saves file with generated name = path returned [OK]

Hint: dest saves file with random name; req.file.path shows saved path [OK]

Common Mistakes:

• Expecting original filename in req.file.path
• Thinking 'dest' is invalid option
• Assuming req.file is undefined without upload

4. Consider this code snippet:

const multer = require('multer');
const upload = multer({ dest: 'uploads/' });

app.post('/upload', upload.single('file'), (req, res) => {
  console.log(req.files);
  res.send('Upload complete');
});

What is the problem with this code?

medium

A. Incorrect destination folder name

B. Using req.files instead of req.file for single file upload

C. Missing call to multer() function

D. upload.single() should be upload.array() for single file

Solution

1. Step 1: Check multer method used

   upload.single('file') handles one file and stores it in req.file (singular).

2. Step 2: Identify incorrect property usage

   The code logs req.files (plural), which is undefined for single file uploads.

3. Final Answer:

   Using req.files instead of req.file for single file upload -> Option B

4. Quick Check:

   single() sets req.file, not req.files [OK]

Hint: Use req.file for single, req.files for multiple uploads [OK]

Common Mistakes:

• Confusing req.file and req.files
• Not calling multer() before .single()
• Using upload.array() when single file expected

5. You want to customize multer to store uploaded files in a folder named 'images' and rename each file to include the current timestamp before the original filename. Which setup correctly achieves this?

hard

A. const storage = multer.diskStorage({ destination: 'images', filename: (req, file, cb) => { cb(null, Date.now() + '-' + file.originalname); } }); const upload = multer({ storage });

B. const storage = multer.diskStorage({ destination: (req, file, cb) => { cb(null, images); }, filename: (req, file, cb) => { cb(null, Date.now() + '-' + file.originalname); } }); const upload = multer({ storage });

C. const storage = multer.diskStorage({ destination: 'images', filename: (req, file, cb) => { cb(null, file.originalname); } }); const upload = multer({ storage });

D. const upload = multer({ dest: 'images', filename: (req, file, cb) => { cb(null, Date.now() + '-' + file.originalname); } });

Solution

1. Step 1: Understand diskStorage options

   diskStorage accepts destination as string or function(req, file, cb); filename must be function(req, file, cb).

2. Step 2: Verify timestamp renaming

   Filename function must call cb(null, Date.now() + '-' + file.originalname).

3. Step 3: Identify correct setup

   const storage = multer.diskStorage({ destination: 'images', filename: (req, file, cb) => { cb(null, Date.now() + '-' + file.originalname); } }); const upload = multer({ storage }); uses valid string destination and correct filename.

4. Final Answer:

   const storage = multer.diskStorage({ destination: 'images', filename: (req, file, cb) => { cb(null, Date.now() + '-' + file.originalname); } }); const upload = multer({ storage }); -> Option A

5. Quick Check:

   destination string + filename(Date.now()) [OK]

Hint: destination: string or fn(); filename: fn() always [OK]

Common Mistakes:

• Using unquoted path in destination function (images vs 'images')
• Passing filename option directly to multer instead of diskStorage
• Not using callback cb in destination or filename