Gets the amount of storage space, in bytes, used one or more items being stored in the storage area.
This function only exists in browser.storage.sync It does not exist in browser.storage.local See https://bugzilla.mozilla.org/show_bug.cgi?id=1385832
This is an asynchronous function that returns a
A key (string) or keys (an array of strings) to identify the item(s) whose storage space you want to retrieve. If an empty array is passed in, 0 will be returned. If you pass
undefinedhere, the function will return the space used by the entire storage area.
Promise that will be fulfilled with an integer,
bytesUsed, representing the storage space used by the objects that were specified in
keys. If the operation failed, the promise will be rejected with an error message.
BCD tables only load in the browser