SSR (Server-Side Rendering) vs CSR (Client-Side Rendering) in Angular

Rendering is the process of converting code into a visible UI in the browser. In Angular, there are two main rendering strategies:

Feature	Server-Side Rendering (SSR)	Client-Side Rendering (CSR)
Where Rendering Happens	On the server before sending to the browser	In the browser after receiving JavaScript
Performance	Faster initial page load	Slower initial load but faster navigation
SEO (Search Engine Optimization)	Better for SEO (search engines can crawl HTML)	Poor SEO (HTML is rendered dynamically)
User Experience	Content is visible immediately	Blank screen or loading indicator before rendering
Use Case	Good for blogs, e-commerce, news sites	Good for web apps like dashboards and SPAs

1️⃣ What is Client-Side Rendering (CSR)?

CSR is the default behavior in Angular applications. The browser downloads a JavaScript bundle, and Angular builds the page dynamically.

CSR Flow

User requests a page → Server sends index.html with a minimal <app-root>.
JavaScript loads → Angular fetches data via API calls.
Angular renders UI → The page becomes interactive.

CSR Example

A typical Angular CSR app (ng new myApp) works like this:

htmlCopyEdit<!-- index.html (Initially) -->
<!DOCTYPE html>
<html>
<head>
  <title>My Angular App</title>
</head>
<body>
  <app-root>Loading...</app-root> <!-- No actual content yet -->
</body>
</html>

👉 The content appears only after Angular loads in the browser.

CSR Pros & Cons

✅ Pros:

Faster navigation between pages after initial load.
More interactive and dynamic.
Works well for SPAs (Single Page Applications).

❌ Cons:

Initial load time is slower.
Bad for SEO because search engines struggle with JavaScript-generated content.

2️⃣ What is Server-Side Rendering (SSR)?

SSR means the server pre-renders the HTML before sending it to the browser. Angular uses Angular Universal for SSR.

SSR Flow

User requests a page → The server processes and renders full HTML.
Browser gets fully rendered HTML → Page appears instantly.
JavaScript loads in background → The app becomes interactive.

SSR Example

With SSR, the server sends a fully-rendered page:

htmlCopyEdit<!-- index.html (Immediately sent to browser) -->
<!DOCTYPE html>
<html>
<head>
  <title>My Angular App</title>
</head>
<body>
  <app-root>
    <h1>Welcome to My Website</h1>
    <p>Latest News...</p>
  </app-root>
</body>
</html>

👉 The user sees content immediately, even before JavaScript loads.

SSR Pros & Cons

✅ Pros:

Faster initial load (good for slow networks).
Great for SEO (search engines can see the full content).
Improved user experience (content appears instantly).

❌ Cons:

More complex setup (requires Angular Universal).
Higher server load (since pages are rendered dynamically).
Slower navigation between pages (since each page is re-rendered on the server).

3️⃣ When to Use SSR vs CSR?

Use Case	Best Rendering Strategy
Blogs, News, E-commerce	✅ SSR (for better SEO and faster load times)
Admin Dashboards, Web Apps	✅ CSR (for better interactivity)
Hybrid Approach	Use SSR for landing pages and CSR for internal pages

4️⃣ How to Enable SSR in Angular?

To enable SSR in an Angular app, use Angular Universal:

shCopyEditng add @nguniversal/express-engine

This adds server-side rendering to your project. You can then run:

shCopyEditnpm run dev:ssr

Key Takeaways

CSR (Client-Side Rendering) → Loads JavaScript first, then renders UI. Good for web apps but bad for SEO.
SSR (Server-Side Rendering) → Pre-renders HTML on the server before sending to the browser. Good for SEO and faster first load.
Use SSR for SEO-heavy sites (e.g., blogs, e-commerce) and CSR for interactive apps (e.g., dashboards, admin panels).

But if SSR also has to call API or perform async tasks, then how is it faster than CSR because in both client side and server side same work is being done?

Let's break it down:

Even though both SSR and CSR make API calls, SSR appears faster because of the way content is delivered to the browser.

1️⃣ CSR (Client-Side Rendering) Process

User requests a page.
Server sends a blank HTML file (index.html) with a <script> tag.
Browser downloads Angular JavaScript bundles.
JavaScript executes in the browser.
API calls are made from the browser.
Once data is received, the UI is finally rendered.

2️⃣ SSR (Server-Side Rendering) Process

User requests a page.
The server makes the API call.
The server pre-renders the HTML with the customer’s data.
Server sends a fully rendered HTML page to the browser.
The browser immediately displays content (even before JavaScript loads).

Key Difference: When the API Call Happens

Rendering Type	Where API Call Happens	When the User Sees Content
CSR	In the browser (after JS loads)	After API response & Angular renders
SSR	On the server (before sending HTML)	Immediately upon receiving HTML

👉 SSR is faster because the user sees content immediately—even if JavaScript hasn’t finished loading.

Real-World Example

Imagine opening an e-commerce website (like Amazon):

With CSR, you first see a loading spinner, then after API calls, the product list appears.
With SSR, the product list is already visible when the page loads.

This is why SSR improves perceived performance and SEO—search engines and users see content faster.

Is SSR Always Faster?

🔹 For static pages: ✅ Yes, SSR is always faster because it serves pre-rendered content.
🔹 For dynamic pages (personalized dashboards, banking apps, etc.): 🚨 SSR still needs API calls, so it may not be significantly faster than CSR.

The host server (where SSR runs) typically has better network conditions and lower latency when calling an API compared to a client’s browser. Here’s why SSR can sometimes be faster than CSR

1️⃣ Faster API Responses on the Server

The server is usually closer (network-wise) to the database or API.
It doesn’t have to deal with slow client-side networks (like mobile data or weak Wi-Fi).
APIs running in the same data center as the SSR server can have very low latency.

🔹 Example: If an Angular SSR app runs on a server in AWS alongside the API, the data retrieval will be much faster than if a client browser in India is fetching data from a US-based API.

2️⃣ No Round Trips Between Browser & API

In CSR, the browser first downloads JavaScript, then makes an API request.
In SSR, the server makes the API request immediately and sends back fully rendered HTML.

This reduces one entire round trip, making SSR faster.

3️⃣ Pre-Rendered HTML Avoids JavaScript Parsing Delay

In CSR, after the API response, Angular still has to process and render the data.
In SSR, the HTML is already rendered, so the browser just displays it.

This makes the page visible instantly.

When SSR May Not Be Faster?

While SSR is great for first-page load, there are some cases where it might not help much:

If the API response itself is slow → SSR won’t magically speed it up.
If the page is highly interactive → After SSR, Angular still has to bootstrap (hydrate) the app, which takes time.
For logged-in users → If every request is personalized, SSR cannot use caching, so it might not be much faster than CSR.

Final Verdict: Is SSR Always Better?

✅ SSR is a better choice if:

You need fast first content load (blogs, news, e-commerce).
SEO is important (search engines can index the pre-rendered content).
Your APIs are fast and close to your SSR server.

🚨 CSR might be better if:

You’re building a highly interactive app (dashboard, admin panel).
Most users navigate after the first page (CSR keeps it smoother)

SSR vs CSR - what is ideal for your scenario?