IDBIndex: unique property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

Note: This feature is available in Web Workers.

The unique read-only property returns a boolean that states whether the index allows duplicate keys.

This is decided when the index is created, using the IDBObjectStore.createIndex method. This method takes an optional parameter, unique, which if set to true means that the index will not be able to accept duplicate entries.

Value

A boolean value:

Value Effect
true The current index does not allow duplicate values for a key.
false The current index allows duplicate key values.

Examples

In the following example we open a transaction and an object store, then get the index lName from a simple contacts database. We then open a basic cursor on the index using IDBIndex.openCursor — this works the same as opening a cursor directly on an ObjectStore using IDBObjectStore.openCursor except that the returned records are sorted based on the index, not the primary key.

The unique status of the index is logged to the console: it should be returned as false.

Finally, we iterate through each record, and insert the data into an HTML table. For a complete working example, see our IndexedDB-examples demo repo (View the example live).

js
function displayDataByIndex() {
  tableEntry.textContent = "";
  const transaction = db.transaction(["contactsList"], "readonly");
  const objectStore = transaction.objectStore("contactsList");

  const myIndex = objectStore.index("lName");
  console.log(myIndex.unique);

  myIndex.openCursor().onsuccess = (event) => {
    const cursor = event.target.result;
    if (cursor) {
      const tableRow = document.createElement("tr");
      for (const cell of [
        cursor.value.id,
        cursor.value.lName,
        cursor.value.fName,
        cursor.value.jTitle,
        cursor.value.company,
        cursor.value.eMail,
        cursor.value.phone,
        cursor.value.age,
      ]) {
        const tableCell = document.createElement("td");
        tableCell.textContent = cell;
        tableRow.appendChild(tableCell);
      }
      tableEntry.appendChild(tableRow);

      cursor.continue();
    } else {
      console.log("Entries all displayed.");
    }
  };
}

Specifications

Specification
Indexed Database API 3.0
# dom-idbindex-unique

Browser compatibility

desktop mobile
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
unique
Chrome – Full support
Chrome 23 (Release date: 2012-11-06)
footnote Full support
Edge – Full support
Edge 12 (Release date: 2015-07-29)
footnote Full support
Firefox – Full support
Firefox 10 (Release date: 2012-01-31)
footnote Full support
Opera – Full support
Opera 15 (Release date: 2013-07-02)
footnote Full support
Safari – Full support
Safari 8 (Release date: 2014-10-16)
footnote Full support
Chrome Android – Full support
Chrome Android 25 (Release date: 2013-02-27)
footnote Full support
Firefox for Android – Full support
Firefox for Android 22 (Release date: 2013-06-25)
footnote Full support
Opera Android – Full support
Opera Android 14 (Release date: 2013-05-21)
footnote Full support
Safari on iOS – Full support
Safari on iOS 8 (Release date: 2014-09-17)
footnote Full support
Samsung Internet – Full support
Samsung Internet 1.5 (Release date: 2013-09-25)
footnote Full support
WebView Android – Full support
WebView Android 4.4 (Release date: 2013-12-09)
footnote Full support
WebView on iOS – Full support
WebView on iOS 8 (Release date: 2014-09-17)
footnote Full support

Legend

Tip: you can click/tap on a cell for more information.

Full support
Full support

See also