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 inWeb Workers.

Theunique read-only property returns a boolean thatstates whether the index allows duplicate keys.

This is decided when the index is created, using theIDBObjectStore.createIndex method. This method takes an optionalparameter,unique, which if set totrue means that the indexwill 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 theindexlName from a simple contacts database. We then open a basic cursor onthe index usingIDBIndex.openCursor — this works the same as opening acursor directly on anObjectStore usingIDBObjectStore.openCursor except that the returned records are sortedbased on the index, not the primary key.

The unique status of the index is logged to the console: it should be returnedasfalse.

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

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.");    }  };}