GET requests in Angular - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What will this Angular component display after a successful GET request?

Consider this Angular standalone component that fetches user data on initialization.

import { Component, OnInit } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-user',
  standalone: true,
  template: `<div>User: {{ user?.name }}</div>`
})
export class UserComponent implements OnInit {
  user: any;
  constructor(private http: HttpClient) {}

  ngOnInit() {
    this.http.get('https://api.example.com/user/1').subscribe(data => {
      this.user = data;
    });
  }
}

Assuming the GET request returns {"name": "Alice"}, what will be shown in the browser?

Angular

import { Component, OnInit } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-user',
  standalone: true,
  template: `<div>User: {{ user?.name }}</div>`
})
export class UserComponent implements OnInit {
  user: any;
  constructor(private http: HttpClient) {}

  ngOnInit() {
    this.http.get('https://api.example.com/user/1').subscribe(data => {
      this.user = data;
    });
  }
}

A User: [object Object]

B User: undefined

C User: null

D User: Alice

💡 Hint

Look at how the template uses the safe navigation operator ?. and what the GET request returns.

The GET request returns an object with a name property set to "Alice". The template safely accesses user?.name, so it displays "User: Alice" once the data arrives.

📝 Syntax

intermediate

Which option correctly performs a GET request using Angular's HttpClient?

Choose the code snippet that correctly uses Angular's HttpClient to perform a GET request and subscribe to the response.

A this.http.get('url').then(response => console.log(response));

B this.http.get('url').on('response', res => console.log(res));

C this.http.get('url').subscribe(response => console.log(response));

D this.http.get('url').fetch(response => console.log(response));

💡 Hint

Remember that Angular's HttpClient returns an Observable, not a Promise.

Angular's HttpClient returns an Observable, so you use subscribe() to get the response. Options A, C, and D use invalid methods.

🔧 Debug

advanced

Why does this Angular GET request fail with a CORS error?

Look at this Angular service method:

getData() {
  return this.http.get('https://external-api.com/data');
}

When called, the browser console shows a CORS error. What is the most likely cause?

Angular

getData() {
  return this.http.get('https://external-api.com/data');
}

A The external API does not allow cross-origin requests from your app's domain.

B The URL is missing the HTTP protocol prefix.

C Angular HttpClient requires POST method for external APIs.

D The HttpClient module is not imported in the app module.

💡 Hint

CORS errors happen when the server blocks requests from different origins.

CORS (Cross-Origin Resource Sharing) errors occur because the external API server does not permit requests from your app's domain. This is a server-side configuration issue.

❓ state_output

advanced

What is the value of 'data' after this GET request completes?

Given this Angular component code:

data: any;

constructor(private http: HttpClient) {}

ngOnInit() {
  this.http.get('https://api.example.com/items').subscribe(response => {
    this.data = response;
  });
}

If the API returns [{"id":1,"name":"Item1"},{"id":2,"name":"Item2"}], what will data contain?

Angular

data: any;

constructor(private http: HttpClient) {}

ngOnInit() {
  this.http.get('https://api.example.com/items').subscribe(response => {
    this.data = response;
  });
}

A {"id":1,"name":"Item1"}

B [{"id":1,"name":"Item1"},{"id":2,"name":"Item2"}]

C undefined

D null

💡 Hint

The API returns an array of objects. The subscription assigns the whole response to data.

The GET request returns an array of two objects. The data variable holds the entire array after subscription.

🧠 Conceptual

expert

Which statement best explains Angular's HttpClient GET request behavior?

Choose the statement that correctly describes how Angular's HttpClient GET requests work.

A HttpClient GET returns an Observable that emits the response once and completes automatically.

B HttpClient GET returns a Promise that resolves with the response data.

C HttpClient GET returns an Observable that keeps emitting data every second until unsubscribed.

D HttpClient GET returns a synchronous response immediately without waiting.

💡 Hint

Think about how Angular handles HTTP requests and Observables.

Angular's HttpClient GET returns an Observable that emits the HTTP response once and then completes. It does not emit repeatedly or return a Promise.

Practice

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

easy

A. To update existing data on the server

B. To send new data to the server

C. To delete data from the server

D. To retrieve data from a server without changing it

Solution

1. Step 1: Understand GET request purpose

   GET requests are used to ask the server to send data without modifying it.

2. Step 2: Compare with other HTTP methods

   POST sends new data, DELETE removes data, PUT/PATCH updates data, so they are not GET.

3. Final Answer:

   To retrieve data from a server without changing it -> Option D

4. Quick Check:

   GET = retrieve data [OK]

Hint: GET always fetches data without changing it [OK]

Common Mistakes:

• Confusing GET with POST or DELETE
• Thinking GET modifies server data
• Using GET to send data in the request body

2. Which of the following is the correct way to make a GET request using Angular's HttpClient?

easy

A. this.http.get('url').subscribe(data => console.log(data));

B. this.http.post('url').subscribe(data => console.log(data));

C. this.http.delete('url').subscribe(data => console.log(data));

D. this.http.put('url').subscribe(data => console.log(data));

Solution

1. Step 1: Identify HttpClient method for GET

   The method to fetch data is get() on HttpClient.

2. Step 2: Check syntax with subscribe

   Using subscribe handles the asynchronous response correctly.

3. Final Answer:

   this.http.get('url').subscribe(data => console.log(data)); -> Option A

4. Quick Check:

   HttpClient.get() + subscribe = correct GET syntax [OK]

Hint: Use http.get() with subscribe to fetch data [OK]

Common Mistakes:

• Using post(), delete(), or put() instead of get()
• Forgetting to subscribe to the observable
• Calling get() without parentheses

3. What will be logged to the console when this Angular code runs?

this.http.get('https://api.example.com/items').subscribe(data => console.log(data));

medium

A. The data received from the API endpoint

B. An error message because subscribe is missing

C. Nothing, because get() does not return data

D. A syntax error due to wrong method usage

Solution

1. Step 1: Understand HttpClient.get() behavior

   The get() method returns an observable that emits the data from the API.

2. Step 2: Effect of subscribe()

   Calling subscribe() listens to the observable and runs the callback with the data, logging it.

3. Final Answer:

   The data received from the API endpoint -> Option A

4. Quick Check:

   subscribe logs API data [OK]

Hint: subscribe callback logs the fetched data [OK]

Common Mistakes:

• Assuming get() returns data directly without subscribe
• Thinking subscribe is optional
• Confusing observable with promise

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

this.http.get('https://api.example.com/data').subscribe(data => this.data = data);

Assuming this.http is properly injected and data is a class property.

medium

A. GET request URL is invalid

B. HttpClient is not imported

C. Missing error handling in subscribe

D. subscribe callback uses wrong arrow function syntax

Solution

1. Step 1: Check syntax and usage

   The get() call and subscribe syntax are correct, and this.http is assumed injected.

2. Step 2: Identify missing best practice

   No error handling is provided in subscribe, which can cause silent failures.

3. Final Answer:

   Missing error handling in subscribe -> Option C

4. Quick Check:

   Always add error handling in subscribe [OK]

Hint: Always handle errors in subscribe to catch failures [OK]

Common Mistakes:

• Ignoring error callback in subscribe
• Assuming URL is invalid without checking
• Confusing arrow function syntax

5. You want to load a list of users from an API and display them in your Angular component. Which approach correctly combines GET request and updating the component's state?

hard

A. Call this.http.post('api/users').subscribe(users => this.users = users); in constructor

B. Use this.http.get('api/users').subscribe(users => this.users = users); in ngOnInit

C. Assign this.users = this.http.get('api/users'); directly without subscribe

D. Use this.http.delete('api/users').subscribe(users => this.users = users); in ngOnInit

Solution

1. Step 1: Choose correct HTTP method and lifecycle hook

   GET is used to fetch data; ngOnInit is the right place to load data after component creation.

2. Step 2: Use subscribe to update component state

   Subscribe receives data asynchronously and assigns it to this.users for display.

3. Final Answer:

   Use this.http.get('api/users').subscribe(users => this.users = users); in ngOnInit -> Option B

4. Quick Check:

   GET + subscribe + ngOnInit = correct pattern [OK]

Hint: Load data in ngOnInit with http.get() and subscribe [OK]

Common Mistakes:

• Using POST or DELETE instead of GET
• Assigning observable directly without subscribe
• Loading data in constructor instead of ngOnInit