javascript - What's the difference between key and primaryKey in IDBCursor of IndexedDB - Stack Overflow

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The documentation here says that

key

Returns the cursor's current key. (Cursors also have a key and a value which represent the key and the value of the last iterated record.)

primaryKey

Returns the cursor's current effective key. (If the source of a cursor is an object store, the effective object store of the cursor is that object store and the effective key of the cursor is the cursor's position.)

In the examples below however the two are used exactly the same and I get the same values for both:

So what is the practical difference?

The documentation here says that

key

Returns the cursor's current key. (Cursors also have a key and a value which represent the key and the value of the last iterated record.)

primaryKey

Returns the cursor's current effective key. (If the source of a cursor is an object store, the effective object store of the cursor is that object store and the effective key of the cursor is the cursor's position.)

In the examples below however the two are used exactly the same and I get the same values for both:

• https://developer.mozilla/en-US/docs/Web/API/IDBCursor/primaryKey
• https://developer.mozilla/en-US/docs/Web/API/IDBCursor/key

So what is the practical difference?

• javascript
• indexeddb

Share Improve this question Follow edited Jun 22, 2016 at 14:47 uberlaufer asked Jun 22, 2016 at 14:31 uberlauferuberlaufer 26122 silver badges88 bronze badges

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1 Answer 1

Sorted by: Reset to default 10

If you're iterating over an object store, they are the same.

If you are iterating over an index, the key is the index key and the primaryKey is the key in the object store.

For example:

 book_store = db.createObjectStore('books');
 title_index = store.createIndex('by_title', 'title');

 key = 123;
 value = {title: 'IDB for Newbies', author: 'Alice'};
 book_store.put(value, key);

 book_store.openCursor().onsuccess = function(e) {
   cursor = e.target.result;
   console.log(cursor.key); // logs 123
   console.log(cursor.primaryKey); // logs 123
 };
 title_index.openCursor().onsuccess = function(e) {
   cursor = e.target.result;
   console.log(cursor.key); // logs 'IDB for Newbies'
   console.log(cursor.primaryKey); // logs 123
 };

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