HTML Code
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>IndexedDB partial update</title>
  <style>
    body { font-family: system-ui, sans-serif; margin: 1.5rem; line-height: 1.5; }
    button { margin-right: 0.5rem; margin-bottom: 0.5rem; padding: 0.5rem 0.9rem; cursor: pointer; }
    #status { margin-top: 1rem; }
  </style>
</head>
<body>
  <h1>get-modify-put</h1>
  <p>Update only the email without wiping other fields.</p>

  <button type="button" id="seedBtn" disabled>Seed id 1</button>
  <button type="button" id="partialBtn" disabled>Change email</button>
  <button type="button" id="getBtn" disabled>Read id 1</button>

  <p id="status">Opening database&hellip;</p>

  <script>
    var statusEl = document.getElementById('status');
    var db;

    var openReq = indexedDB.open('tryitUpdatePartial', 1);

    openReq.onupgradeneeded = function (event) {
      event.target.result.createObjectStore('contacts', { keyPath: 'id' });
    };

    openReq.onsuccess = function (event) {
      db = event.target.result;
      statusEl.textContent = 'Ready.';
      ['seedBtn', 'partialBtn', 'getBtn'].forEach(function (id) {
        document.getElementById(id).disabled = false;
      });
    };

    document.getElementById('seedBtn').addEventListener('click', function () {
      var tx = db.transaction(['contacts'], 'readwrite');
      tx.objectStore('contacts').put({
        id: 1,
        name: 'Alex Rivera',
        email: 'alex@example.com',
        city: 'Chennai'
      });
      tx.oncomplete = function () {
        statusEl.textContent = 'Seeded with city Chennai.';
      };
    });

    document.getElementById('partialBtn').addEventListener('click', function () {
      var tx = db.transaction(['contacts'], 'readwrite');
      var store = tx.objectStore('contacts');

      store.get(1).onsuccess = function (event) {
        var contact = event.target.result;
        if (!contact) {
          statusEl.textContent = 'Not found. Seed first.';
          return;
        }
        contact.email = 'new@example.com';
        store.put(contact);
      };

      tx.oncomplete = function () {
        statusEl.textContent = 'Email updated; city kept.';
      };
    });

    document.getElementById('getBtn').addEventListener('click', function () {
      var tx = db.transaction(['contacts'], 'readonly');
      var req = tx.objectStore('contacts').get(1);
      req.onsuccess = function () {
        var c = req.result;
        if (!c) {
          statusEl.textContent = 'Not found.';
          return;
        }
        statusEl.textContent = c.name + ' | ' + c.email + ' | ' + c.city;
      };
    });
  </script>
</body>
</html>
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IndexedDB Update — get-modify-put
