Database Node.js Server API - UpdateDocument function

Is there a way to add items to an array in a relationship?

I am currently trying this where tasks are a One To Many relationship attribute represented as an array
const item = await databases .updateDocument([DATABASE_ID], [collection_id], [documentId], { tasks: [taskId] })
When I try this I only get that item added to the array and previous additions removed.

i dont think adding an item to an array is possible directly atm. you must get the array value, append your item and then update the doc.