Liveview on page load - is there a way to hook into the router?

Phoenix Forum Questions / Help
1

I’m trying to send analytics events between LiveViews loads. Is there a way to hook into the router?

2

Yup, group your LiveView routes into live session(s) via Phoenix.LiveView.Router.live_session/3 and then use its :on_mount option to attach one or more hooks to the mount lifecycle of each LiveView in the session.

Here’s an example from the Phoenix.LiveView.on_mount/1 docs:

# lib/my_app_web/live/init_assigns.ex
defmodule MyAppWeb.InitAssigns do
  @moduledoc """
  Ensures common `assigns` are applied to all LiveViews attaching this hook.
  """
  import Phoenix.LiveView
  import Phoenix.Component

  def on_mount(:default, _params, _session, socket) do
    {:cont, assign(socket, :page_title, "DemoWeb")}
  end
  ...
end

# lib/my_app_web/router.ex
defmodule MyAppWeb.Router do
  use MyAppWeb, :router

  # pipelines, plugs, etc.

  live_session :default, on_mount: MyAppWeb.InitAssigns do
    scope "/", MyAppWeb do
      pipe_through :browser
      live "/", PageLive, :index
    end
  end
  ...
end
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3

Oh thought on_mount was fired once per “live_session”. I’ll have to dig into that.

4

Yup, one of featured use cases for on_mount is handling auth across LiveView redirects which don’t get pipe_throughed the usual auth plugs that typically gets fired once before the stateful connection is established.

Once again, it is worth remembering that LiveViews require their own security checks, so we use pipe_through above to protect the regular routes (get, post, etc.) and the LiveViews should run their own checks using on_mount hooks.
…
Finally, you can even combine live_session with on_mount. Instead of declaring on_mount on every LiveView, you can declare it at the router level and it will enforce it on all LiveViews under it:

source: Security considerations of the LiveView model: live_session and live_redirect

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