PUT and PATCH route handling in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a PUT route handler for updating a user.

Express

app.[1]('/user/:id', (req, res) => {
  // update user logic
  res.send('User updated');
});

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

Apost

Bput

Cdelete

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using GET or POST instead of PUT for updating resources.

Confusing DELETE with update operations.

The PUT method is used to update a resource completely. Here, app.put defines the route handler for PUT requests.

2fill in blank

medium

Complete the code to create a PATCH route handler for partially updating a user.

Express

app.[1]('/user/:id', (req, res) => {
  // partial update logic
  res.send('User partially updated');
});

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

Apatch

Bpost

Cput

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using PUT instead of PATCH for partial updates.

Using GET or POST for update operations.

PATCH is used for partial updates of a resource. Here, app.patch defines the route handler for PATCH requests.

3fill in blank

hard

Fix the error in the route handler method to correctly handle a PUT request.

Express

app.[1]('/product/:id', (req, res) => {
  // update product logic
  res.send('Product updated');
});

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

Apatch

Bpost

Cget

Dput

Attempts:

3 left

💡 Hint

Common Mistakes

Using PATCH or POST instead of PUT for full updates.

Using GET which is for fetching data.

The route must use put to handle PUT requests for updating the product.

4fill in blank

hard

Fill both blanks to create a PATCH route that updates only the user's email.

Express

app.[1]('/user/:id', (req, res) => {
  const newEmail = req.body.[2];
  // update email logic
  res.send('Email updated');
});

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

Apatch

Bput

Cemail

Dusername

Attempts:

3 left

💡 Hint

Common Mistakes

Using PUT instead of PATCH for partial updates.

Accessing the wrong property like username instead of email.

The route uses patch for partial update, and email is the field to update from the request body.

5fill in blank

hard

Fill all three blanks to create a PUT route that updates a product's name and price.

Express

app.[1]('/product/:id', (req, res) => {
  const updatedName = req.body.[2];
  const updatedPrice = req.body.[3];
  // update product logic
  res.send('Product updated with new name and price');
});

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

Aput

Bname

Cprice

Dpatch

Attempts:

3 left

💡 Hint

Common Mistakes

Using PATCH instead of PUT for full updates.

Mixing up property names or using incorrect ones.

The route uses put for full update, and accesses name and price from the request body to update the product.

Practice

1. What is the main difference between PUT and PATCH methods in Express route handling?

easy

A. PUT updates only specified fields, while PATCH replaces the entire resource.

B. PUT replaces the entire resource, while PATCH updates only specified fields.

C. PUT is used only for creating resources, PATCH for deleting.

D. PUT and PATCH behave exactly the same in Express.

Solution

1. Step 1: Understand HTTP method semantics

   PUT is designed to replace the entire resource with the new data sent in the request.

2. Step 2: Understand PATCH behavior

   PATCH updates only the fields specified in the request, leaving other fields unchanged.

3. Final Answer:

   PUT replaces the entire resource, while PATCH updates only specified fields. -> Option B

4. Quick Check:

   PUT replaces, PATCH updates partial [OK]

Hint: Remember: PUT replaces all, PATCH changes parts only [OK]

Common Mistakes:

• Confusing PUT and PATCH behavior
• Thinking PATCH deletes resources
• Assuming PUT only updates parts

2. Which of the following is the correct way to define a PATCH route in Express to update a user by ID?

easy

A. app.get('/user/:id', (req, res) => { /* update logic */ });

B. app.put('/user/:id', (req, res) => { /* update logic */ });

C. app.patch('/user/:id', (req, res) => { /* update logic */ });

D. app.post('/user/:id', (req, res) => { /* update logic */ });

Solution

1. Step 1: Identify the HTTP method for partial updates

   PATCH is used to update parts of a resource, so the route should use app.patch.

2. Step 2: Check route syntax

   The route path includes /:id to specify which user to update, and the handler function is correctly defined.

3. Final Answer:

   app.patch('/user/:id', (req, res) => { /* update logic */ }); -> Option C

4. Quick Check:

   PATCH route uses app.patch() [OK]

Hint: PATCH routes use app.patch(path, handler) syntax [OK]

Common Mistakes:

• Using app.put instead of app.patch for partial updates
• Using app.get or app.post incorrectly
• Missing route parameter syntax

3. Given this Express code snippet, what will be the response after a PATCH request to /product/5 with JSON body {"price": 20}?

const products = { 5: { name: "Pen", price: 10, stock: 100 } };
app.patch('/product/:id', (req, res) => {
  const id = req.params.id;
  Object.assign(products[id], req.body);
  res.json(products[id]);
});

medium

A. {"name":"Pen","price":20,"stock":100}

B. {"name":"Pen","price":10,"stock":100}

C. {"price":20}

D. Error: Cannot read property 'price' of undefined

Solution

1. Step 1: Understand the initial product data

   Product with ID 5 has name "Pen", price 10, and stock 100.

2. Step 2: Analyze the PATCH handler logic

   The handler uses Object.assign to update the product with fields from req.body. The JSON body contains {"price": 20}, so only the price changes.

3. Final Answer:

   {"name":"Pen","price":20,"stock":100} -> Option A

4. Quick Check:

   PATCH updates price only, other fields stay same [OK]

Hint: PATCH merges fields; unchanged fields remain [OK]

Common Mistakes:

• Expecting full replacement of product data
• Ignoring unchanged fields
• Assuming error due to missing fields

4. What is wrong with this Express PUT route handler?

app.put('/item/:id', (req, res) => {
  const id = req.params.id;
  items[id] = req.body;
  res.send('Item updated');
});

Assuming items is an object storing item data.

medium

A. The route path is missing a trailing slash.

B. The route should use PATCH instead of PUT.

C. The response should be JSON, not plain text.

D. It does not parse JSON body, so req.body will be undefined.

Solution

1. Step 1: Check if JSON body parsing middleware is used

   Without express.json() middleware, req.body will be undefined for JSON requests.

2. Step 2: Identify the impact on the handler

   Assigning items[id] = req.body will set the item to undefined, causing data loss or errors.

3. Final Answer:

   It does not parse JSON body, so req.body will be undefined. -> Option D

4. Quick Check:

   Missing express.json() causes undefined req.body [OK]

Hint: Always use express.json() to read JSON request bodies [OK]

Common Mistakes:

• Forgetting to add express.json() middleware
• Confusing PUT and PATCH usage
• Ignoring response content type

5. You want to implement a PUT route to replace a user profile but keep the id field unchanged. Which approach correctly handles this in Express?

hard

A. Overwrite the entire user object with req.body except manually set id back after assignment.

B. Use PATCH instead of PUT to update only the fields except id.

C. Reject the PUT request if id is present in req.body.

D. Delete the user first, then create a new user with req.body including id.

Solution

1. Step 1: Understand PUT semantics

   PUT replaces the entire resource, so the user object will be overwritten by req.body.

2. Step 2: Preserve the id field

   Since id should not change, after overwriting, manually set user.id back to the original value.

3. Final Answer:

   Overwrite the entire user object with req.body except manually set id back after assignment. -> Option A

4. Quick Check:

   PUT replaces all; preserve id manually [OK]

Hint: PUT replaces all; reset id manually after update [OK]

Common Mistakes:

• Using PATCH when full replacement is needed
• Allowing id to be overwritten unintentionally
• Deleting and recreating user unnecessarily