SPA vs SSR (and more)

Modern UI frameworks (React/Vue/...) enable a wide range of render modes:

  • SPA
  • SSR
  • Pre-rendering (aka SSG)
  • HTML-only

We compare these render modes with each other and explain which render mode should be used when.

See Guides > Render Modes (SPA, SSR, SSG, HTML-only) for how to use render modes with your vite-plugin-ssr app.

Technical Overview

Technically and precisely speaking, the difference between each render mode is the following.

  • SSR: the page is rendered twice. It's rendered to HTML on the server-side as well as rendered (hydrated) on the browser-side. (The page is loaded both in Node.js and in the browser.)
  • SPA: the page is only rendered in the browser. The page's content is not rendered to HTML. (The page is loaded only in the browser.)
  • HTML-only: the page is rendered only on the server-side (to HTML). It's not rendered in the browser and has zero/minimal browser-side JavaScript. (The page is loaded only in Node.js.)
  • Pre-rendering (aka SSG): the page is rendered to HTML at build-time (instead of request-time).

SPA

SPA means that the page is loaded & rendered only in the browser.

In general, if our page:

  1. doesn't need SEO (e.g. an Admin Panel doesn't need to appear in Google searches), and
  2. mobile performance is not crucial (e.g. the user is expected to use the Admin Panel on a desktop device)

then SPA is an option.

SPA advantages:

  • Our page's code doesn't need to be able to run in Node.js. For example, SPA is the only option for UI libraries that don't work with SSR.

    Most libraries nowadays support SSR (or have workarounds).

  • SPA doesn't enforce the usage of a production Node.js server: SPAs can be deployed to a static host.

    We can remove the need for a production Node.js server for SSR apps by using pre-rendering.

  • Decreased backend workload.

While for certain types of pages, such as an Admin Panel where there is a clear choice in favor of SPA, there often isn't a clear cut whether we should use SPA or SSR.

SSR

SSR means that our page is rendered to HTML as well as as rendered (hydrated) in the browser.

It is the most capable mode as it enables:

  • Improved SEO (e.g. high ranking on Google)
  • Improved mobile performance

For example, social news websites need SSR. (They are interactive while needing both SEO and mobile performance.)

SSR improves mobile performance in the sense that the page's content is rendered to HTML and can already be shown to the user before the browser-side JavaScript even starts loading. (Loading & executing JavaScript is usually very slow on mobile.)

For pages that are not content centric (e.g. a to-do list app) and don't need SEO, we can consider SPA instead of SSR.

Pre-rendering

Pre-rendering means to render the page's HTML at build-time instead of request-time.

We should use pre-rendering whenever we can, as it allows us to deploy our app to a Static Host.

For example, https://vite-plugin-ssr.com is pre-rendered and deployed to GitHub Pages.

See Guides > Pre-rendering (SSG).

HTML-only

HTML-only means that the page is only loaded & rendered on the server-side.

For content centric pages with no/little interactivity (the page has no/few stateful components), then using HTML-only is an option.

Examples:

  • Blog
  • Portfolio/homepage
  • Marketing pages
  • Software Documentation (e.g. https://vite-plugin-ssr.com)

The advantage of HTML-only is that the page has no/little browser-side JavaScript, which leads to considerably faster loading times (especially on mobile).

For the few bits of interactivity (such as an image carousel or a collapsible section), the page can load a couple of vanilla browser-side JavaScript libraries to surgically implement these few bits of interactivity. This is what https://vite-plugin-ssr.com does: if we inspect the browser-side JavaScript of this page, we'll see only around 1-2KB of JavaScript.

SSG

Tools that pre-render pages are also known as "SSG" (Static-Site Generators).

In the context of vite-plugin-ssr, we use the terms "SSG" and "pre-rendering" interchangeably.

See Guides > Pre-rendering (SSG).