SharedStorage: append() method

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The append() method of the SharedStorage interface appends a string to the value of an existing key-value pair in the current origin's shared storage.


append(key, value)



A string representing the key of the key-value pair to which you want to append a value.


A string that you want to append to the existing value of the key-value pair.

Note: If the specified key isn't found in the shared storage, the append() operation is equivalent to set(), that is, a new key-value pair with the specified key is added to the shared storage.

Return value

A Promise that fulfills with undefined.


  • The Promise rejects with a TypeError if:
    • The appended entry was not successfully stored in the database due to shared storage not being available (for example it is disabled using a browser setting).
    • key and/or value exceed the browser-defined maximum length.
    • The calling site does not have the Shared Storage API included in a successful privacy sandbox enrollment process.
  • In the case of WorkletSharedStorage, the Promise rejects with a TypeError if the worklet module has not been added with SharedStorageWorklet.addModule().

Note: In the case of WindowSharedStorage, if the append() operation doesn't successfully write to the database for a reason other than shared storage not being available, no error is thrown — the operation still fulfills with undefined.


  .append("integer-list", ",9")
  .then(console.log("Value appended to integer list"));


Shared Storage API
# dom-sharedstorage-append

Browser compatibility

BCD tables only load in the browser

See also