Setting headers and params in Angular

Introduction

Headers and params help you send extra information with your web requests. This lets servers know what you want or how to handle your request.

When you need to send an API key or token to access protected data.

When you want to filter or sort data by sending query parameters.

When you want to tell the server the type of data you accept or send.

When you want to customize requests with language or format preferences.

When you want to send pagination info like page number or size.

Syntax

Angular

const headers = new HttpHeaders({ 'Header-Name': 'value' });
const params = new HttpParams().set('paramName', 'paramValue');

this.http.get(url, { headers, params });

Use HttpHeaders to set request headers as key-value pairs.

Use HttpParams to add query parameters to the URL.

Examples

Sends a GET request with an Authorization header carrying a token.

Angular

const headers = new HttpHeaders({ 'Authorization': 'Bearer token123' });
this.http.get('/api/data', { headers });

Sends a GET request with query parameters page=2 and limit=10 to control pagination.

Angular

const params = new HttpParams().set('page', '2').set('limit', '10');
this.http.get('/api/items', { params });

Sends a POST request with JSON content type header and a search query parameter.

Angular

const headers = new HttpHeaders().set('Content-Type', 'application/json');
const params = new HttpParams().set('search', 'book');
this.http.post('/api/search', { data: 'example' }, { headers, params });

Sample Program

This Angular component has a button. When clicked, it sends a GET request with an Authorization header and two query parameters. The response is shown below the button in JSON format.

Angular

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

@Component({
  selector: 'app-root',
  template: `<button (click)="fetchData()">Fetch Data</button><pre>{{response | json}}</pre>`
})
export class AppComponent {
  response: any;

  constructor(private http: HttpClient) {}

  fetchData() {
    const headers = new HttpHeaders().set('Authorization', 'Bearer mytoken123');
    const params = new HttpParams().set('category', 'books').set('limit', '5');

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

Important Notes

Headers and params are immutable. Use set or append methods to create new instances.

Always encode params properly; Angular's HttpParams handles this automatically.

Use headers to send tokens or content types; use params for filtering or pagination.

Summary

Headers add extra info to requests, like tokens or content types.

Params add query data to URLs, like filters or page numbers.

Use Angular's HttpHeaders and HttpParams classes to set them cleanly.

Practice

1. What is the main purpose of setting headers in an Angular HTTP request?

easy

A. To change the URL of the request

B. To add extra information like authentication tokens or content type

C. To modify the HTTP method (GET, POST, etc.)

D. To handle the response data format

Solution

1. Step 1: Understand what headers do

   Headers carry extra info like tokens or content type in HTTP requests.

2. Step 2: Compare options

   Only To add extra information like authentication tokens or content type correctly describes headers' purpose; others describe different concepts.

3. Final Answer:

   To add extra information like authentication tokens or content type -> Option B

4. Quick Check:

   Headers add info = A [OK]

Hint: Headers carry extra info like tokens, not URL or method [OK]

Common Mistakes:

• Confusing headers with URL parameters
• Thinking headers change HTTP method
• Assuming headers handle response data

2. Which of the following is the correct way to add a header named Authorization with value Bearer token123 using Angular's HttpHeaders?

easy

A. new HttpHeaders().set('Authorization', 'Bearer token123')

B. new HttpHeaders('Authorization', 'Bearer token123')

C. HttpHeaders.append('Authorization', 'Bearer token123')

D. HttpHeaders.add('Authorization', 'Bearer token123')

Solution

1. Step 1: Recall HttpHeaders usage

   HttpHeaders is immutable; use set method to add headers.

2. Step 2: Check each option

   Only new HttpHeaders().set('Authorization', 'Bearer token123') uses new HttpHeaders().set() correctly; others are invalid syntax or methods.

3. Final Answer:

   new HttpHeaders().set('Authorization', 'Bearer token123') -> Option A

4. Quick Check:

   Use set() on new HttpHeaders() = B [OK]

Hint: Use new HttpHeaders().set() to add headers [OK]

Common Mistakes:

• Trying to pass headers directly to constructor
• Using non-existent methods like append or add
• Not creating a new HttpHeaders instance first

3. Given the code below, what will be the final URL requested?

const params = new HttpParams().set('page', '2').set('sort', 'name');
this.http.get('/api/items', { params }).subscribe();

medium

A. /api/items

B. /api/items?sort=name&page=2

C. /api/items?page=2

D. /api/items?page=2&sort=name

Solution

1. Step 1: Understand HttpParams chaining

   Each set returns a new HttpParams with added param; chaining adds both params.

2. Step 2: Determine param order

   Params appear in order set: page=2 then sort=name.

3. Final Answer:

   /api/items?page=2&sort=name -> Option D

4. Quick Check:

   Params chained = URL with both params in order [OK]

Hint: Chained set() adds params in order to URL [OK]

Common Mistakes:

• Assuming only last set param remains
• Ignoring param order in URL
• Forgetting to pass params in request options

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

const headers = new HttpHeaders();
headers.set('Content-Type', 'application/json');
this.http.post('/api/data', body, { headers }).subscribe();

medium

A. Headers must be plain object, not HttpHeaders instance

B. Missing import for HttpHeaders

C. HttpHeaders is immutable; set() does not change original headers

D. post() method requires params object

Solution

1. Step 1: Understand HttpHeaders immutability

   HttpHeaders methods like set return new instances; original is unchanged.

2. Step 2: Analyze code behavior

   Headers remain empty because set result is not assigned back.

3. Final Answer:

   HttpHeaders is immutable; set() does not change original headers -> Option C

4. Quick Check:

   HttpHeaders immutable = assign set() result [OK]

Hint: Assign set() result to headers variable [OK]

Common Mistakes:

• Not assigning set() result back
• Assuming headers object changes in place
• Confusing HttpHeaders with plain objects

5. You want to send a GET request with headers { 'Authorization': 'Bearer abc123' } and query params { 'filter': 'active', 'limit': '10' }. Which code correctly sets both headers and params in Angular?

hard

A. const headers = new HttpHeaders({ Authorization: 'Bearer abc123' });
const params = new HttpParams({ fromObject: { filter: 'active', limit: '10' } });
this.http.get('/api/users', { headers, params }).subscribe();

B. const headers = new HttpHeaders('Authorization', 'Bearer abc123');
const params = { filter: 'active', limit: '10' };
this.http.get('/api/users', { headers, params }).subscribe();

C. const headers = new HttpHeaders();
headers.set('Authorization', 'Bearer abc123');
const params = new HttpParams().set('filter', 'active').set('limit', '10');
this.http.get('/api/users', { headers, params }).subscribe();

D. const headers = new HttpHeaders().add('Authorization', 'Bearer abc123');
const params = new HttpParams().add('filter', 'active').add('limit', '10');
this.http.get('/api/users', { headers, params }).subscribe();

Solution

1. Step 1: Check header creation

   HttpHeaders constructor accepts a plain object like { Authorization: 'Bearer abc123' } for initial headers.

2. Step 2: Check params creation

   HttpParams constructor accepts { fromObject: { filter: 'active', limit: '10' } } to set multiple params at once.

3. Step 3: Verify request call

   Both headers and params are passed correctly in the request options { headers, params }.

4. Final Answer:

   Use HttpHeaders({ Authorization: 'Bearer abc123' }) and HttpParams({ fromObject: { filter: 'active', limit: '10' } }) -> Option A

5. Quick Check:

   Use constructors with objects for headers and params = C [OK]

Hint: Use HttpHeaders({}) and HttpParams({fromObject:{}}) for multiple values [OK]

Common Mistakes:

• Wrong constructor arguments or plain objects without proper instances
• Not assigning set() result due to immutability
• Using non-existent methods like add()