Lazy Load Images Sketch

Lazy Load Images Sketch: free step-by-step lesson with examples, common mistakes, and interview tips — part of jQuery Tutorial on Toolliyo Academy.

8 min read Updated 8/22/2026

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jQuery Tutorial · Lesson 65 of 100

Lazy Load Images Sketch

Setup & DOM ✓ → Events Effects AJAX ✓ → Perf & Integrate → Ship & Projects

Perf & Integrate · 3 — Harden · ~10 min · Performance and Security

What is this?

Lazy loading defers offscreen images until needed. Sketch: mark imgs with data-src, then swap to src when near the viewport using scroll/intersection checks.

Why should you care?

QueryVerse media-heavy catalogs on 4G India networks benefit from fewer eager downloads.

See it live — copy this example

Examples include the jQuery 3.7 CDN. Paste into an HTML file or use Run Example to preview.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>QueryVerse</title>
  <style>
    body { font-family: system-ui, sans-serif; margin: 1.25rem; }
    .box { padding: .75rem; border: 1px solid #ccc; border-radius: 8px; margin: .5rem 0; }
    .muted { color: #666; }
    button { margin-right: .35rem; margin-top: .35rem; }
    input, select, textarea { margin: .25rem 0; }
    table { border-collapse: collapse; width: 100%; }
    th, td { border: 1px solid #ddd; padding: .4rem .55rem; text-align: left; }
    .hidden { display: none; }
    .row-odd { background: #f7f7f7; }
    .active { font-weight: 700; }
    .toast { background: #111; color: #fff; padding: .5rem .75rem; border-radius: 6px; }
  </style>
</head>
<body>
  <p class="muted">Scroll stub — click to simulate entering viewport</p>
  <img id="pic" alt="Product" data-src="https://via.placeholder.com/120x80.png?text=QV" width="120" height="80" style="background:#eee">
  <button type="button" id="enter">Simulate enter viewport</button>
  <p id="out" class="muted"></p>
<script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
<script>
$(function () {
  $('#enter').on('click', function () {
    var $img = $('#pic');
    var src = $img.attr('data-src');
    if (!src || $img.attr('src')) { $('#out').text('Already loaded or missing data-src'); return; }
    $img.attr('src', src);
    $('#out').text('Loaded from data-src');
  });
});
</script>
</body>
</html>

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>QueryVerse</title>
  <style>
    body { font-family: system-ui, sans-serif; margin: 1.25rem; }
    .box { padding: .75rem; border: 1px solid #ccc; border-radius: 8px; margin: .5rem 0; }
    .muted { color: #666; }
    button { margin-right: .35rem; margin-top: .35rem; }
    input, select, textarea { margin: .25rem 0; }
    table { border-collapse: collapse; width: 100%; }
    th, td { border: 1px solid #ddd; padding: .4rem .55rem; text-align: left; }
    .hidden { display: none; }
    .row-odd { background: #f7f7f7; }
    .active { font-weight: 700; }
    .toast { background: #111; color: #fff; padding: .5rem .75rem; border-radius: 6px; }
  </style>
</head>
<body>
  <p class="muted">Scroll stub — click to simulate entering viewport</p>
  <img id="pic" alt="Product" data-src="https://via.placeholder.com/120x80.png?text=QV" width="120" height="80" style="background:#eee">
  <button type="button" id="enter">Simulate enter viewport</button>
  <p id="out" class="muted"></p>
<script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
<script>
$(function () {
  $('#enter').on('click', function () {
    var $img = $('#pic');
    var src = $img.attr('data-src');
    if (!src || $img.attr('src')) { $('#out').text('Already loaded or missing data-src'); return; }
    $img.attr('src', src);
    $('#out').text('Loaded from data-src');
  });
});
</script>
</body>
</html>

Result