Issues found

The main reason my code didn’t work was because my disable_button? function was returning "false" instead of false. To be more precise:

So, in Phoenix LV, if the value is false the attribute disabled is removed from the node, while if it is any other thing (like "false"), the node gets the attribute as disabled=“something else”, which means that because disabled is still present, irrespective of value, it is considered as a disabled button.

This differs from the behaviour in the browser, where if I add disable="false" the browser will not consider the node disabled.

Source: Enable/disable a button in Phoenix 1.7 depending on state - #6 by Fl4m3Ph03n1x - Questions / Help - Elixir Programming Language Forum

Another issue is that this function also needs to return a value that depends on the state itself. In this case I am generating a random number, which is independent of state, thus the button would never update.

Answer

So, for those who are curious, this is the code I ended up with:

core_components.ex

This is my modified button function:

  @doc """
  Renders a button.

  ## Examples

      <.button>Send!</.button>
      <.button phx-click="go" class="ml-2" disabled=false>Send!</.button>
  """
  attr :type, :string, default: nil
  attr :class, :string, default: nil
  attr :disabled, :boolean, default: false
  attr :rest, :global, include: ~w(form name value)

  slot :inner_block, required: true

  def button(assigns) do
    ~H"""
    <button
      type={@type}
      class={if @disabled do
      [
        "rounded-md bg-slate-400 px-3 py-2 text-sm font-semibold text-white shadow-sm",
        @class
      ]
    else
      [
        "phx-submit-loading:opacity-75 rounded-md bg-indigo-600 px-3 py-2 text-sm font-semibold text-white shadow-sm",
        "hover:bg-indigo-500 active:text-white/80",
        @class
      ]
    end}
      {@rest}
      disabled={@disabled}
    >
      <%= render_slot(@inner_block) %>
    </button>
    """
  end

And here is how I use it:

my_app_live.html.heex

<.button class="min-w-full" disabled={disable_button?(@param1, @state)}>Execute Command</.button>

This depends on the state, because the state changes with time, which means my button’s appearance will also change with time!