Keeping the socket out of async tasks

If your assign_async/3 callback reads socket.assigns.user_id, it captures the whole socket, even though the query only needs an ID:

# Captures the socket
assign_async(socket, :user, fn ->
  {:ok, %{user: Accounts.get_user!(socket.assigns.user_id)}}
end)

# Extract the ID before creating the callback
user_id = socket.assigns.user_id

assign_async(socket, :user, fn ->
  {:ok, %{user: Accounts.get_user!(user_id)}}
end)

The second callback captures user_id, so the task receives that value instead of the socket and its other assigns.

Moving the assignment inside the callback won’t help, because the function still captures socket. Extract what you need before fn ->. The same applies to callbacks passed to start_async/3 and Task.async/1.

https://hexdocs.pm/phoenix_live_view/Phoenix.LiveView.html#module-async-operations