DELETE route handling in Express - Mini Project: Build & Apply

DELETE Route Handling in Express

📖 Scenario: You are building a simple Express server to manage a list of books. Users can add, view, and delete books. Now, you will add the ability to delete a book by its ID using a DELETE route.

🎯 Goal: Create an Express DELETE route that removes a book from the list by its id.

📋 What You'll Learn

Create an array called books with three book objects, each having id and title properties.

Create a variable called bookIdToDelete and set it to 2.

Use the filter method on books to remove the book with id equal to bookIdToDelete.

Add an Express DELETE route at /books/:id that deletes the book with the given id from books.

💡 Why This Matters

🌍 Real World

Deleting items from a list via an API is common in web apps, such as removing products from a shopping cart or deleting user posts.

💼 Career

Understanding how to handle DELETE routes in Express is essential for backend web development roles that build RESTful APIs.

1

Create the initial books array

Create an array called books with these exact objects: { id: 1, title: 'Book One' }, { id: 2, title: 'Book Two' }, and { id: 3, title: 'Book Three' }.

Express

# Your code here

Hint

Use const books = [ ... ] with three objects inside.

2

Set the book ID to delete

Create a variable called bookIdToDelete and set it to the number 2.

Express

const books = [
  { id: 1, title: 'Book One' },
  { id: 2, title: 'Book Two' },
  { id: 3, title: 'Book Three' }
];

# Your code here

Hint

Use const bookIdToDelete = 2; to store the ID.

3

Filter out the book to delete

Use the filter method on books to create a new array without the book whose id matches bookIdToDelete. Assign this new array back to books.

Express

const books = [
  { id: 1, title: 'Book One' },
  { id: 2, title: 'Book Two' },
  { id: 3, title: 'Book Three' }
];

const bookIdToDelete = 2;

# Your code here

Hint

Use books = books.filter(book => book.id !== bookIdToDelete); to remove the book.

4

Add the Express DELETE route

Add an Express DELETE route at /books/:id. Inside the route handler, convert req.params.id to a number, then update books by filtering out the book with that id. Send a JSON response with { message: 'Book deleted' }.

Express

let books = [
  { id: 1, title: 'Book One' },
  { id: 2, title: 'Book Two' },
  { id: 3, title: 'Book Three' }
];

const bookIdToDelete = 2;

books = books.filter(book => book.id !== bookIdToDelete);

// Your code here

Hint

Use app.delete('/books/:id', (req, res) => { ... }) and inside convert req.params.id to a number, then filter books, then send JSON response.

Practice

1. What is the main purpose of a DELETE route in Express?

easy

A. To update existing data on the server

B. To add new data to the server

C. To remove data from the server

D. To retrieve data from the server

Solution

1. Step 1: Understand HTTP methods

   HTTP methods define actions: GET retrieves, POST adds, PUT updates, DELETE removes.

2. Step 2: Identify DELETE route purpose

   DELETE routes specifically handle requests to remove data from the server.

3. Final Answer:

   To remove data from the server -> Option C

4. Quick Check:

   DELETE = remove data [OK]

Hint: DELETE routes always remove data from the server [OK]

Common Mistakes:

• Confusing DELETE with POST or GET
• Thinking DELETE adds or updates data
• Assuming DELETE retrieves data

2. Which of the following is the correct syntax to define a DELETE route for path /items/:id in Express?

easy

A. app.delete('/items/:id', (req, res) => { /* handler */ });

B. app.get('/items/:id', (req, res) => { /* handler */ });

C. app.post('/items/:id', (req, res) => { /* handler */ });

D. app.put('/items/:id', (req, res) => { /* handler */ });

Solution

1. Step 1: Identify HTTP method for deletion

   DELETE method is used to remove resources, so app.delete is correct.

2. Step 2: Check route path and handler syntax

   The path /items/:id with a callback function matches Express route syntax.

3. Final Answer:

   app.delete('/items/:id', (req, res) => { /* handler */ }); -> Option A

4. Quick Check:

   DELETE route syntax = app.delete(path, handler) [OK]

Hint: Use app.delete for DELETE routes, not get/post/put [OK]

Common Mistakes:

• Using app.get or app.post instead of app.delete
• Missing the callback function
• Incorrect path format

3. What will be the response if the following Express DELETE route is called with DELETE /users/5 and the user with id 5 exists?

const users = [{id: 1}, {id: 5}, {id: 9}];
app.delete('/users/:id', (req, res) => {
  const id = Number(req.params.id);
  const index = users.findIndex(u => u.id === id);
  if (index !== -1) {
    users.splice(index, 1);
    res.status(200).send('User deleted');
  } else {
    res.status(404).send('User not found');
  }
});

medium

A. Response status 200 with message 'User deleted'

B. Response status 404 with message 'User not found'

C. Response status 500 with server error

D. Response status 200 with message 'User not found'

Solution

1. Step 1: Check if user with id 5 exists

   The array contains {id: 5}, so index will not be -1.

2. Step 2: Analyze response when user found

   Since index !== -1, user is removed and response status 200 with 'User deleted' is sent.

3. Final Answer:

   Response status 200 with message 'User deleted' -> Option A

4. Quick Check:

   User exists = 200 'User deleted' [OK]

Hint: If item found, DELETE route sends 200 with success message [OK]

Common Mistakes:

• Assuming 404 even if user exists
• Confusing status codes
• Not converting id to number before comparison

4. Identify the error in this DELETE route code snippet:

app.delete('/products/:id', (req, res) => {
  const id = req.params.id;
  const product = products.find(p => p.id === id);
  if (!product) {
    res.status(404).send('Product not found');
  }
  products = products.filter(p => p.id !== id);
  res.send('Product deleted');
});

medium

A. Incorrect route path syntax

B. Missing callback function in app.delete

C. id is not converted to number before comparison

D. res.send called twice without return

Solution

1. Step 1: Check flow after 404 response

   If product not found, res.status(404).send is called but code continues without return.

2. Step 2: Identify multiple responses sent

   After 404 response, code still filters products and calls res.send again, causing error.

3. Final Answer:

   res.send called twice without return -> Option D

4. Quick Check:

   Multiple res.send calls without return cause errors [OK]

Hint: Use return after sending response to avoid multiple sends [OK]

Common Mistakes:

• Not returning after sending 404 response
• Ignoring type conversion for id
• Assuming route path is wrong

5. You want to create a DELETE route that removes a book by its ID from a nested data structure where books are grouped by genre. Which approach correctly handles deletion and sends a 404 if the book is not found?

const library = {
  fiction: [{id: 1, title: 'A'}, {id: 2, title: 'B'}],
  nonFiction: [{id: 3, title: 'C'}]
};

app.delete('/books/:id', (req, res) => {
  const id = Number(req.params.id);
  let found = false;
  for (const genre in library) {
    const index = library[genre].findIndex(book => book.id === id);
    if (index !== -1) {
      library[genre].splice(index, 1);
      found = true;
      break;
    }
  }
  if (found) {
    res.status(200).send('Book deleted');
  } else {
    res.status(404).send('Book not found');
  }
});

hard

A. The code does not break after deletion, causing multiple deletions

B. This code correctly deletes the book and handles 404 if not found

C. The code misses converting id to number, causing no matches

D. The code sends 200 status even if book is not found

Solution

1. Step 1: Check id conversion

   id is converted to Number, ensuring correct comparison with book ids.

2. Step 2: Verify loop and deletion logic

   Loop checks each genre, finds book by id, deletes it, sets found true, and breaks loop to avoid extra deletions.

3. Step 3: Confirm response handling

   If found is true, sends 200 with 'Book deleted'; else sends 404 with 'Book not found'.

4. Final Answer:

   This code correctly deletes the book and handles 404 if not found -> Option B

5. Quick Check:

   Proper id conversion, deletion, and response = correct code [OK]

Hint: Convert id, break loop after deletion, send 404 if not found [OK]

Common Mistakes:

• Not converting id to number before comparison
• Not breaking loop after deletion
• Sending success response even if book missing