The following javascript types are possible to index:

• number
• Date
• string
• ArrayBuffer
• Typed arrays (Uint8Array, Float32Array, …, etc)
• Arrays of (strings, numbers, Dates, ArrayBuffer, Typed array) or a mix of those.

Note that all other types are non-indexable, including:

• boolean
• undefined
• Object
• null

Type order

Index keys of different types can be compared against each other. The following order applies:

1. -Infinity
2. number
3. Infinity
4. Date
5. string
6. TypedArray and ArrayBuffer
7. Arrays

Lowest and Highest possible keys

• The lowest possible value is -Infinity. Dexie has an alias for it: Dexie.minKey.
• There is theoretically no highest possible value as Array may contain Arrays of Arrays etc… But Dexie provide an alias for the practical maximum key Dexie.maxKey = [[]] (an array of an array).

See also

https://w3c.github.io/IndexedDB/#key-type

Sample

const db = new Dexie('testdb');
db.version(1).stores({
    foo: 'id,bar'
});

db.foo.put({id: null}); // fails with DataError because null is not indexable.
db.foo.put({id: 1, bar: null}); // succeeds but fails silently to be indexed by "bar" index.
db.foo.where('bar').equals(undefined).toArray(); // Fails with DataError as undefined is not indexable.