Function inject_key_into_value 

pub(crate) fn inject_key_into_value(
    cx: &mut JSContext,
    value: HandleValue<'_>,
    key: &IndexedDBKeyType,
    key_path: &DOMString,
) -> Result<bool, Error>

https://w3c.github.io/IndexedDB/#inject-a-key-into-a-value-using-a-key-path