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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>IndexedDB ConstraintError</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>ConstraintError demo</h1>
  <p>First add succeeds. Second add with the same key fails.</p>

  <button type="button" id="add1Btn" disabled>1. add() id 1</button>
  <button type="button" id="add2Btn" disabled>2. add() id 1 again</button>
  <button type="button" id="clearBtn" disabled>Clear store</button>

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

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

    function addContact() {
      var tx = db.transaction(['contacts'], 'readwrite');
      var req = tx.objectStore('contacts').add({
        id: 1,
        name: 'Alex Rivera'
      });

      req.onsuccess = function () {
        statusEl.textContent = 'Added id ' + req.result;
      };

      req.onerror = function () {
        if (req.error && req.error.name === 'ConstraintError') {
          statusEl.textContent = 'Key already exists: 1 (ConstraintError)';
        } else {
          statusEl.textContent = 'Error: ' + (req.error && req.error.message);
        }
      };
    }

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

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

    openReq.onsuccess = function (event) {
      db = event.target.result;
      statusEl.textContent = 'Ready.';
      ['add1Btn', 'add2Btn', 'clearBtn'].forEach(function (id) {
        document.getElementById(id).disabled = false;
      });
    };

    document.getElementById('add1Btn').addEventListener('click', addContact);
    document.getElementById('add2Btn').addEventListener('click', addContact);

    document.getElementById('clearBtn').addEventListener('click', function () {
      var tx = db.transaction(['contacts'], 'readwrite');
      tx.objectStore('contacts').clear();
      tx.oncomplete = function () {
        statusEl.textContent = 'Store cleared. Try add() again.';
      };
    });
  </script>
</body>
</html>
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IndexedDB Insert — ConstraintError on Duplicate add()
