Rendering Modes Explained

In this article, we will explore the different rendering modes for a web application, commonly seen in meta-frameworks like Next.js and Nuxt. Understanding these modes is crucial for developers seeking to optimize performance and user experience.

For demonstration purposes, we will use a project I've developed in Nuxt 3, which makes it easier to see the differences between the rendering modes.

Client-Side Rendering (CSR)

Modern JavaScript libraries and frameworks like Vue.js and React.js brought many improvements to the front-end ecosystem, such as easier componentization and a reactivity system, but they also introduced their own challenges.

When we talk about Client-Side Rendering (CSR), it's how those frameworks typically operate by default. Rendering occurs entirely on the client-side, within the browser. This means that the server delivers a blank page and then the JavaScript needs to be downloaded and executed to render the UI to the user. Consequently, there's a period during which the user sees no content, which can vary based on the user's network speed and hardware.

In addition to the poor user experience inherent in this rendering mode, SEO is also impacted because web crawlers must wait for the page to be fully rendered before they can index it.

This mode is also commonly referred to as SPA (Single Page Application).

Pros:

Lesser complexity
Can be hosted on a static server

Cons:

Blank page while JavaScript is not executed
Bad for SEO

Demonstration

Server-Side Rendering (SSR)

The meta-frameworks were created to mainly solve that problem. When we talk about “meta-framework”, it usually means a framework that is built on top of another, providing further abstraction and tools. For example, Next.js is a meta-framework for React.js and Nuxt is a meta-framework for Vue.js.

How they solve that problem is by introducing Server-Side Rendering (SSR). When the browser requests a page from the server, instead of the server responding with a blank page, it runs the framework on the server-side to render the page. This means that the user doesn't see a blank page anymore, but a fully-rendered page without executing any JavaScript on the browser.

Of course, that page is completely static, so there's no interactivity. The process of turning the static page into an interactive page is called hydration. Basically, what this means is that the framework is run again on the browser side, so it binds all the event listeners in the DOM and makes the page interactive.

An important point to understand is that usually, our API calls need to be made on the server so that the data is present to render the page. The meta-frameworks usually introduce some sort of hook or function that makes all those requests run on the server and not be duplicated in the client.

Pros:

Good for SEO
Page content available immediately

Cons:

Greater complexity
Needs a server with support
Bigger processing cost

Demonstration

Static Site Generation (SSG)

Another feature that the meta-frameworks introduced is Static Site Generation (SSG). Static means that the page doesn't depend on any dynamic data.

For example, imagine a profile page. A profile page should not be static because the content of the page is different based on the user details. On the other hand, a page that describes the terms and conditions of your application is always going to be the same, because it doesn't have any dynamic data that needs to be fetched on the server-side.

For those cases, it's a good option to opt for SSG. Those pages are going to be rendered at build time and will not change, so the server uses fewer resources to deliver those pages to the client.

Pros:

Good for SEO
Page content available immediately
Can be hosted on a static server

Cons:

Greater complexity
Limitation with dynamic route parameters
Dynamic content not updated after build

Demonstration

Incremental Static Regeneration (ISR)

The last option and the most recent one introduced by meta-frameworks is Incremental Static Regeneration (ISR). One easy way to describe it is that it is a mix of SSR and SSG because it renders the page, caches it, and revalidates it after a specific time interval.

For example, imagine a page with the most recent blog posts. New posts aren't created every second, so it makes sense to render the page, cache it, and after 1 minute re-render the page. While the TTL (Time To Live) doesn't expire, the server will deliver the cached page.

When using ISR, it's up to you to define the TTL of the page, so choose a setting that makes sense for the page in question.

Other terms that may be used are: Incremental Static Generation (ISG) and Stale-While-Revalidate (SWR).