POST requests in Angular - Performance & Optimization

Performance: POST requests

MEDIUM IMPACT

POST requests affect the time it takes to send data to the server and receive a response, impacting interaction responsiveness and perceived speed.

Sending form data to the server without blocking the UI

Angular

this.isLoading = true;
this.http.post('/api/data', largePayload).subscribe({
  next: response => { this.processResponse(response); },
  complete: () => { this.isLoading = false; },
  error: () => { this.isLoading = false; }
}); // shows loading state and provides feedback

Shows loading state and provides feedback to keep UI feeling responsive.

📈 Performance Gainimproves INP by providing feedback and preventing multiple submissions

Sending form data to the server without blocking the UI

Angular

this.http.post('/api/data', largePayload).subscribe(response => { this.processResponse(response); }); // no loading state or user feedback

This does not provide feedback, causing the UI to feel unresponsive until the request completes.

📉 Performance CostUI feels unresponsive during request, increases INP

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
POST without UI feedback	Minimal	0	Low but UI feels unresponsive	[X] Bad
Asynchronous POST with loading state	Minimal	0	Low and non-blocking	[OK] Good

Rendering Pipeline

POST requests run asynchronously outside the rendering pipeline but can affect rendering if UI updates wait for the response.

→Composite

→Paint

⚠️ BottleneckUI feeling unresponsive while waiting for POST response

Core Web Vital Affected

INP

POST requests affect the time it takes to send data to the server and receive a response, impacting interaction responsiveness and perceived speed.

Optimization Tips

1Provide loading indicators for all POST requests to improve perceived responsiveness.

2Show loading indicators during POST requests to improve user feedback.

3Keep POST payloads small to reduce network delay and improve responsiveness.

Performance Quiz - 3 Questions

What is the main performance risk of sending large POST requests without loading states in Angular?

A It causes layout shifts (CLS) during rendering.

B It increases the page's Largest Contentful Paint (LCP).

C It causes the UI to feel unresponsive, causing slow interaction response.

D It reduces the bundle size.

DevTools: Network

How to check: Open DevTools, go to Network tab, filter by XHR, and observe POST request timing and size.

What to look for: Look for long request durations or large payload sizes that delay response and affect interaction speed.