why phoenix liveview update/assign message make client contenteditable value revert?

Question

With Phoenix live view document I add a live page for writing a realtime form app. There is very simple demo:

<h2>Hello</h2>

Counter is222: <%= @counter %>
<hr>

<button phx-click="dec">-</button>
<button phx-click="inc">+</button>

<table border="1">
  <tr>
    <th contenteditable="true">Month</th>
    <th>S1</th>
    <th>S2</th>
  </tr>
  <tr>
    <td contenteditable="true">January</td>
    <td contenteditable="true">$100</td>
    <td contenteditable="true">$10220</td>
  </tr>
</table>

Server side code (just like document):

defmodule TicTacWeb.MemberSchedulerLive do
  use Phoenix.LiveView


  def render(assigns) do
    TicTacWeb.PageView.render("member_scheduler.html", assigns)
  end

  def mount(_, socket) do
    {:ok, assign(socket, %{counter: 100})}
  end

  def handle_event("inc", _, socket) do
    {:noreply, update(socket, :counter, fn(x) -> x + 1 end)}
  end

  def handle_event("dec", _, socket) do
    IO.puts("item")
    {:noreply, update(socket, :counter, fn(x) -> x - 1 end)}
  end

end

The problem is <td contenteditable value will be revert after I click - or + emit a message to server.

1. why - or + affect <td> 's value? Is't minimize change modified dom data?
2. Is there a best practice for such scene?

Thanks!

UPDATE
After add contenteditable as data model, it was still not work, such as:
1. html snippet

    ....
    <td contenteditable="true">$100</td>
    <td contenteditable="true" phx-blur="somedata"><%=@somedata%></td>
  </tr>
</table>

2. backend

  ...
  def mount(_, socket) do
    {:ok, assign(socket, %{counter: 100, somedata: "$001"})}
  end

The @somedata also revert to $001 if click - or + .

Answer 1

why - or + affect <td> 's value?

It's vice versa. They do not affect <td> 's value, on the contrary, it sends the diff between the previous state and the updated state and the frontend applies this diff .

LiveView has no idea about your local changes with the contenteditable="true" and hence it resets everything to its original state, save for :counter that gets updated. To support contenteditable="true" you need to make these <td> 'sa part of data model so that LiveView is aware about the changes in there.

Answer 2

I finally solve the problem by two step:

1. add phx-update='ignore' and the contenteditable will not be update!
   In this stage, it's <td contenteditable="true" phx-update='ignore'>$10220</td>

2. update phoenix_live_view to 0.4.1 which was github: phoenixframework/phoenix_live_view (locked commit is: 73e9a695eff1d7d21e4cb34ea9894835b3a2fa32) and the old version seems not support phx-update

Hope it also could be help you.

Thanks @Aleksei Matiushkin, I will dive into liveview diff algorithm.