PUT and DELETE requests in Angular - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of a PUT request in Angular?

A PUT request is used to update an existing resource on the server with new data. It replaces the entire resource with the data sent.

beginner

How does a DELETE request work in Angular's HttpClient?

A DELETE request tells the server to remove a specific resource identified by a URL. It usually does not send a body, just the resource identifier.

intermediate

Show the Angular HttpClient method signature for making a PUT request.

httpClient.put<T>(url: string, body: any, options?: {...}): Observable<T>

beginner

What is a common use case for DELETE requests in Angular apps?

Deleting a user, post, or item from a list by sending a DELETE request to the server with the item's ID in the URL.

intermediate

Why should you handle errors when making PUT or DELETE requests in Angular?

Because the server might reject the request or fail, so handling errors helps show messages to users and keep the app stable.

Which Angular HttpClient method is used to update an existing resource?

A put()

B post()

C get()

D delete()

The put() method updates an existing resource by replacing it with new data.

What does a DELETE request typically include?

A A full data body to update

B Authentication token only

C A URL identifying the resource

D A list of resources

DELETE requests usually include the URL of the resource to remove, without a data body.

In Angular, what does the put() method return?

A An Observable of the server response

B A Promise of the request

C A direct data object

D Nothing

Angular's HttpClient methods return Observables to handle asynchronous data streams.

Why is error handling important for PUT and DELETE requests?

A To encrypt the data

B To inform users if the request fails

C To cache the response

D To speed up the request

Error handling helps show messages or retry logic if the server rejects the request.

Which HTTP method should you use to remove a resource in Angular?

A GET

B PUT

C POST

D DELETE

DELETE is the standard HTTP method to remove a resource.

Explain how to make a PUT request in Angular and why you would use it.

Think about replacing data on the server.

Describe the process and purpose of a DELETE request in Angular applications.

Focus on removing items from the server.

Practice

1. What is the main purpose of a PUT request in Angular's HttpClient?

easy

A. To retrieve data from the server

B. To delete a resource from the server

C. To update an existing resource by sending the full new data

D. To partially update a resource

Solution

1. Step 1: Understand HTTP methods

   PUT is used to update or replace an existing resource completely.

2. Step 2: Compare with other methods

   DELETE removes data, GET retrieves data, PATCH partially updates data.

3. Final Answer:

   To update an existing resource by sending the full new data -> Option C

4. Quick Check:

   PUT updates full resource = A [OK]

Hint: PUT replaces full data, DELETE removes resource [OK]

Common Mistakes:

• Confusing PUT with DELETE
• Thinking PUT partially updates data
• Mixing GET with PUT

2. Which of the following is the correct syntax to send a DELETE request using Angular's HttpClient?

easy

A. this.http.delete('api/items/1').subscribe();

B. this.http.put('api/items/1').subscribe();

C. this.http.get('api/items/1').subscribe();

D. this.http.post('api/items/1').subscribe();

Solution

1. Step 1: Identify the method for DELETE

   Angular's HttpClient uses delete() to send DELETE requests.

2. Step 2: Check syntax correctness

   The method call this.http.delete('api/items/1').subscribe(); correctly sends a DELETE request and subscribes to the response.

3. Final Answer:

   this.http.delete('api/items/1').subscribe(); -> Option A

4. Quick Check:

   DELETE method uses http.delete() [OK]

Hint: Use http.delete() for DELETE requests [OK]

Common Mistakes:

• Using http.put() instead of http.delete()
• Forgetting to subscribe to the observable
• Using http.post() for deleting

3. Given this Angular code snippet, what will be logged after the PUT request completes successfully?

const updatedItem = { id: 5, name: 'New Name' };
this.http.put('api/items/5', updatedItem).subscribe(response => {
  console.log(response);
});

medium

A. The updated item object returned from the server

B. An error message because PUT requires no body

C. Nothing, because PUT does not return data

D. The original item before update

Solution

1. Step 1: Understand PUT request behavior

   PUT sends the full updated data and usually returns the updated resource from the server.

2. Step 2: Analyze the subscription callback

   The response logged is the server's reply, typically the updated item object.

3. Final Answer:

   The updated item object returned from the server -> Option A

4. Quick Check:

   PUT returns updated data = A [OK]

Hint: PUT usually returns updated resource in response [OK]

Common Mistakes:

• Assuming PUT returns no data
• Confusing PUT with DELETE response
• Expecting original item instead of updated

4. Identify the error in this Angular DELETE request code:

this.http.delete('api/items').subscribe(response => {
  console.log('Item deleted');
});

Assuming the API requires an item ID to delete a specific item.

medium

A. DELETE requests cannot be sent without a request body

B. The URL is missing the item ID to specify which item to delete

C. The subscribe method is missing a parameter

D. The console.log statement is incorrect

Solution

1. Step 1: Check the URL for DELETE request

   The URL 'api/items' does not specify which item to delete; an ID is needed.

2. Step 2: Understand API requirements

   APIs usually require an ID in the URL like 'api/items/1' to delete a specific item.

3. Final Answer:

   The URL is missing the item ID to specify which item to delete -> Option B

4. Quick Check:

   DELETE URL needs item ID = C [OK]

Hint: DELETE URL must include resource ID to delete [OK]

Common Mistakes:

• Sending DELETE without specifying resource ID
• Thinking DELETE needs a request body
• Ignoring subscribe callback

5. You want to update a user's profile and then delete their old profile picture in Angular. Which sequence of HttpClient calls correctly applies PUT and DELETE requests?

// Update user profile
this.http.put('api/users/10', updatedUser).subscribe(() => {
  // Delete old profile picture
  this.http.delete('api/pictures/oldPicId').subscribe(() => {
    console.log('Profile updated and old picture deleted');
  });
});

hard

A. DELETE request first to delete picture, then PUT request inside DELETE's subscribe to update profile

B. Use only PUT request to update profile and delete picture together

C. Send PUT and DELETE requests simultaneously without waiting for response

D. PUT request first to update profile, then DELETE request inside PUT's subscribe to delete picture

Solution

1. Step 1: Understand request order

   First update the user profile with PUT, then delete the old picture after success.

2. Step 2: Analyze code structure

   DELETE request is inside PUT's subscribe callback, ensuring sequential execution.

3. Step 3: Evaluate other options

   Deleting first may remove picture before profile update; simultaneous calls lack order; PUT cannot delete picture.

4. Final Answer:

   PUT request first to update profile, then DELETE request inside PUT's subscribe to delete picture -> Option D

5. Quick Check:

   Update then delete sequentially = B [OK]

Hint: Chain DELETE inside PUT subscribe for correct order [OK]

Common Mistakes:

• Deleting before updating causing data mismatch
• Sending requests simultaneously without order
• Trying to delete picture with PUT request