ISR vs SSG — When Your App Wants to Sleep but SEO Won’t Let It

🧠 Frontend Wars: ISR vs SSG — When Your App Wants to Sleep but SEO Won’t Let It

Welcome back, brave developer!
Last time, we battled SSR vs CSR, a war between servers and browsers that left many laptops overheating and many devs emotionally scarred.

Today’s fight?
It’s between two cousins who love caching but can’t agree on when to wake up:
ISR (Incremental Static Regeneration) and SSG (Static Site Generation).

Grab your coffee — this one’s about performance, laziness, and SEO guilt. ☕

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🏕️ First, SSG — The Overachiever Who Never Changes

Static Site Generation (SSG) means your pages are generated at build time — long before any user visits.

Imagine you bake 1,000 muffins in the morning (HTML pages), and when people visit, you just hand them one.
Fast, efficient, and no stress. 🍰

Example:

# next.config.js
export async function getStaticProps() {
  const posts = await getAllPosts();
  return { props: { posts } };
}

When you deploy, all your pages are ready-made HTML.
Your CDN loves you, your users love you, and your backend server is asleep.

✅ Pros:

• Lightning-fast load times (no server rendering at runtime)
• Cheap hosting (CDN handles it)
• Great SEO

❌ Cons:

• You need to rebuild to update data
• Large sites = long build times
• Feels outdated if your data changes often (e.g., news, stock prices, or your mood)

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⏰ Then, ISR — The Lazy Genius Who Updates Later

Incremental Static Regeneration (ISR) is like SSG’s chill cousin who says:

“Hey, what if I don’t rebuild everything, just the stuff that changed?”

Instead of regenerating all pages every time, ISR allows static pages to update on demand — after deployment.

Example with Next.js:

export async function getStaticProps() {
  const data = await fetchData();
  return {
    props: { data },
    revalidate: 60, // re-generate this page every 60 seconds
  };
}

That revalidate: 60 line?
It’s like setting a reminder:

“Yo server, refresh this page once a minute — but only if someone visits.”

So your content stays fresh without full rebuilds.
Basically, ISR is lazy but responsible.

✅ Pros:

• Still static (fast)
• Auto-refreshes data (SEO-friendly)
• Scales like a champ

❌ Cons:

• Stale data between regenerations
• Slight delay on the first re-render
• Debugging can be... spiritually challenging

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⚔️ ISR vs SSG — The Epic Face-Off

Feature	SSG	ISR
Page generation	Build time	On-demand (after deploy)
Performance	⚡ Instant	⚡ Still instant
Data freshness	🧊 Frozen in time	🧃 Refreshes automatically
Build time	🐢 Can be long	🚀 Much faster
Ideal for	Blogs, docs, marketing pages	News sites, product catalogs, dashboards

So:

• SSG: “I did all my work before anyone came.”
• ISR: “I’ll update when I feel like it.”

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🧙‍♂️ When to Use Which

• Use SSG when:
  You have stable content (blog posts, docs, landing pages).

• Use ISR when:
  You want fast pages and occasional freshness (product listings, blog homepages, event calendars).

• Don’t use either when:
  Your data changes every few seconds — use SSR or Edge Rendering instead (coming in Episode 3 😏).

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💡 Real-World Example

Let’s say you’re building a sneaker site.

• The homepage and about page? → SSG (they rarely change).
• The product listing page? → ISR, so new sneakers appear automatically.
• The checkout page? → Definitely SSR, because it depends on user sessions and inventory.

Boom 💥 — hybrid architecture, modern as your favorite JS meme.

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🎯 TL;DR

• SSG = Build once, serve forever.
• ISR = Build once, revalidate sometimes.
• SSR = Build every time, if you hate caching.
• CSR = Build nothing on the server, let the browser suffer.

If your app content rarely changes → SSG.
If it changes often → ISR.
If you like chaos → CSR + random API calls.

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😂 Final Thoughts

ISR and SSG aren’t enemies — they’re just different levels of caffeine tolerance.

• SSG is that person who wakes up at 5 AM and finishes all their work before breakfast.
• ISR wakes up at noon, updates stuff when necessary, and still gets great results.

And both are still faster than your typical “Loading…” spinner built with pure CSR.

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Next time on Frontend Wars:

🧩 Hydration Hell — Why React Yells at You After SSR (and how to survive it with your sanity intact).

Don’t miss it. Hydration errors are like mosquitoes — tiny but ruin your whole evening.

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