Migrate Away Piecemeal

Migrate Away Piecemeal: free step-by-step lesson with examples, common mistakes, and interview tips — part of jQuery Tutorial on Toolliyo Academy.

8 min read Updated 8/23/2026

On this page

jQuery Tutorial · Lesson 85 of 100

Migrate Away Piecemeal

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

Ship & Projects · 4 — Build · ~10 min · Debug and Modernize

What is this?

Do not rewrite the whole QueryVerse UI at once. Replace one widget with vanilla or a framework island, keep jQuery elsewhere, and share data via APIs/DOM events.

Why should you care?

Big-bang migrations fail under business pressure; strangler patterns succeed.

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>
  <div id="legacy" class="box">jQuery widget still here</div>
  <div id="island" class="box">Vanilla island</div>
  <button type="button" id="go">Strangle one feature</button>
  <p id="out" class="muted"></p>
<script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
<script>
$(function () {
  $('#legacy').on('click', function () {
    $('#out').text('legacy jQuery path');
  });
  document.getElementById('island').addEventListener('click', function () {
    document.getElementById('out').textContent = 'vanilla island path';
  });
  $('#go').on('click', function () {
    $('#out').text('Plan: move notifications first, leave grid on jQuery');
  });
});
</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>
  <div id="legacy" class="box">jQuery widget still here</div>
  <div id="island" class="box">Vanilla island</div>
  <button type="button" id="go">Strangle one feature</button>
  <p id="out" class="muted"></p>
<script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
<script>
$(function () {
  $('#legacy').on('click', function () {
    $('#out').text('legacy jQuery path');
  });
  document.getElementById('island').addEventListener('click', function () {
    document.getElementById('out').textContent = 'vanilla island path';
  });
  $('#go').on('click', function () {
    $('#out').text('Plan: move notifications first, leave grid on jQuery');
  });
});
</script>
</body>
</html>

Result