Setting headers and params in Angular - Step-by-Step Execution

Concept Flow - Setting headers and params

Create HttpHeaders object

↓

Create HttpParams object

↓

Build HttpRequest with headers and params

↓

Send request via HttpClient

↓

Receive response

↓

Process response

This flow shows how Angular builds an HTTP request by creating headers and parameters, then sends it and processes the response.

Execution Sample

Angular

const headers = new HttpHeaders().set('Authorization', 'Bearer token');
const params = new HttpParams().set('page', '1').set('limit', '10');
this.http.get('/api/items', { headers: headers, params: params }).subscribe(response => {
  console.log(response);
});

This code sets an Authorization header and query parameters page and limit, then sends a GET request and logs the response.

Execution Table

Step	Action	Headers State	Params State	HttpClient Call	Output
1	Create HttpHeaders with Authorization	{Authorization: 'Bearer token'}	{}	No	Headers object created
2	Create HttpParams with page=1	{Authorization: 'Bearer token'}	{page: '1'}	No	Params object created with page
3	Add limit=10 to HttpParams	{Authorization: 'Bearer token'}	{page: '1', limit: '10'}	No	Params object updated with limit
4	Call http.get with headers and params	{Authorization: 'Bearer token'}	{page: '1', limit: '10'}	GET /api/items?page=1&limit=10 with headers	Request sent
5	Receive response	{Authorization: 'Bearer token'}	{page: '1', limit: '10'}	No	Response received and logged
6	End	{Authorization: 'Bearer token'}	{page: '1', limit: '10'}	No	Execution complete

💡 Request sent and response received, process ends

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
headers	{}	{Authorization: 'Bearer token'}	{Authorization: 'Bearer token'}	{Authorization: 'Bearer token'}	{Authorization: 'Bearer token'}
params	{}	{}	{page: '1'}	{page: '1', limit: '10'}	{page: '1', limit: '10'}

Key Moments - 2 Insights

Why do we chain .set() calls on HttpParams instead of calling it once?

HttpParams is immutable; each .set() returns a new object. See execution_table rows 2 and 3 where params updates step-by-step.

Can we modify HttpHeaders or HttpParams after passing them to HttpClient?

No, they are immutable. You must create new instances before the request. The execution_table shows headers and params stay unchanged after the request (rows 4-6).

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the state of params?

A {page: '1'}

B {}

C {page: '1', limit: '10'}

D {limit: '10'}

💡 Hint

Check the Params State column at step 3 in execution_table

At which step is the HTTP GET request actually sent?

A Step 4

B Step 5

C Step 2

D Step 3

💡 Hint

Look for HttpClient Call column indicating request sent

If we forget to assign the result of .set() on HttpParams, what happens?

A Params contain only the last set value

B Params remain empty

C Params contain all values set

D Code throws an error

💡 Hint

Recall that HttpParams is immutable and .set() returns a new object (see key_moments)

Concept Snapshot

Angular HTTP headers and params are immutable objects.
Use .set() to add or update values, assigning the result each time.
Pass headers and params as options in HttpClient methods.
HttpClient sends the request with these included.
Always assign new HttpParams or HttpHeaders after .set() calls.

Full Transcript

In Angular, when setting headers and parameters for HTTP requests, you create HttpHeaders and HttpParams objects. These objects are immutable, so each time you call .set(), you get a new object that you must assign to a variable. After building headers and params, you pass them as options to HttpClient methods like get(). The request is sent with these headers and query parameters included. The response is then received and processed. This flow ensures your HTTP requests have the correct metadata and query data.