Lazy Loading — Complete Guide
Lazy Loading — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of HTML Tutorial on Toolliyo Academy.
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HTML Tutorial · Lesson 71 of 100
Lazy Loading
Basics ✓ → Forms & semantics ✓ → APIs & performance → Projects
APIs & performance · 3 — HTML5, CSS/JS, security · ~10 min · HTML — Performance & Security
What is this?
Lazy loading delays off-screen images and iframes until the user scrolls near them.
Why should you care?
MarkupVerse catalog pages load hero first and defer product thumbnails.
See it live — copy this example
Save as demo.html and open in your browser, or use Run Example below.
<section class="product-grid">
<img src="hero-wallet.jpg" alt="MarkupVerse wallet" width="800" height="400" fetchpriority="high">
<img src="thumb-card.jpg" alt="Platinum card" width="200" height="200" loading="lazy" decoding="async">
<img src="thumb-loan.jpg" alt="Home loan" width="200" height="200" loading="lazy" decoding="async">
</section>Run Example »
Edit the code below and click Run to see the result in Toolliyo’s live editor.
What happened?
- loading="lazy" on below-fold imgs.
- fetchpriority="high" on LCP hero only — don’t overuse.
Practice next
- Mark hero without lazy.
- Add loading=lazy on thumbs.
- Set width/height to reduce CLS.
- Add loading=lazy on iframes.
- Remove lazy on first row only.
Remember
lazy below fold. fetchpriority on hero. Explicit dimensions.
MarkupVerse product grid
Shop page has 40 thumbnails.
Outcome: Initial load skips off-screen images.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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