Understanding Rendering Methods in Next.js: SSG, SSR, ISR, and CSR

Introduction

Next.js is a powerful React framework for building modern web applications. One of its core strengths lies in the flexibility it offers in how web pages are rendered. Choosing the right rendering method is crucial for optimizing performance, SEO, and user experience.

In this blog, we will explore four key rendering methods in Next.js:

1. Static Site Generation (SSG)

2. Server Side Rendering (SSR)

3. Incremental Static Regeneration (ISR)

4. Client Side Rendering (CSR)

We will also look at when to use each, along with a simple flowchart to help you decide.

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1. Static Site Generation (SSG)

SSG generates HTML pages at build time and serves them as static files.
It is ideal for content that does not change frequently or doesn’t require real-time data.
SSG offers excellent performance since pages are pre-rendered.

What it is: The HTML pages are generated at build time and served as static files.

When to use: When the content does not change frequently. Examples include blogs, documentation, marketing pages.

Key Advantage: Fast page loads, great for SEO.

Limitation: If content changes, the site needs to be rebuilt.

2. Server Side Rendering (SSR)

SSR renders the page on the server and sends the complete HTML to the client.

It is ideal when you want to deliver a fully rendered page with content populated from APIs and databases without relying on client-side JavaScript. It allows search engines to crawl and index pages effectively.

What it is: The page is generated on the server for each request.

When to use: When data changes often or is personalized. Examples include dashboards, authenticated content.

Key Advantage: Always serves fresh content.

Limitation: Slightly slower than SSG due to server processing.

3. Incremental Static Regeneration (ISR)

ISR combines the benefits of SSR and SSG by allowing pages to be statically generated at build time and then incrementally regenerated with new data as it becomes available.

It is ideal for content that needs to be frequently updated but doesn’t require real-time rendering.

What it is: Combines the speed of SSG with the ability to update static pages in the background.

When to use: For sites that need occasional updates without a full rebuild. Examples include news sites, product listings.

Key Advantage: Automatic updates while still serving static content.

Limitation: Complex caching behavior in some cases.

4. Client Side Rendering (CSR)

CSR renders the page on the client’s browser using JavaScript.
It is ideal when you have dynamic content that needs to be fetched and rendered after the initial render.
CSR can provide a better user experience by updating only the necessary parts of the page.

What it is: The browser fetches data after the initial page loads, typically using JavaScript.

When to use: For parts of an app that don't need to be indexed by search engines or are highly interactive. Examples include dashboards, user profiles.

Key Advantage: Very dynamic, often faster for logged-in users.

Limitation: Poor initial SEO, slower first load.

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Choosing the Right Rendering Method: Flowchart

1. Does the page need to update frequently?

   • No → Go to Question 2

   • Yes → Use SSR

2. Does the page need to be super fast and SEO-friendly?

   • Yes → Use SSG

3. Does the content change occasionally but not on every request?

   • Yes → Use ISR

4. Is the content highly interactive or personalized?

   • Yes → Use CSR

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Summary Comparison Table