proof of concept: phx-portal

This is a proof of concept commit implementing a new phx binding called
`phx-portal`. This binding allows to designate an element to be rendered
at another location in the DOM, designated by the ID that `phx-portal`
points to. This can be useful to render things like dialogs at the top
layer, outside any containers that might affect their rendering (e.g.
overflow: hidden).

Nowadays there is also the Popover API and native `<dialog>` elements,
so this might not be that important any more.

Because of this, I also don't feel like this is something we really want
to support. This commit only shows how it could be implemented.

assets/js/phoenix_live_view/constants.js

@@ -54,6 +54,8 @@ export const PHX_THROTTLE = "throttle"
 export const PHX_UPDATE = "update"
 export const PHX_STREAM = "stream"
 export const PHX_STREAM_REF = "data-phx-stream"
+export const PHX_PORTAL = "portal"
+export const PHX_PORTAL_REF = "data-phx-portal"
 export const PHX_KEY = "key"
 export const PHX_PRIVATE = "phxPrivate"
 export const PHX_AUTO_RECOVER = "auto-recover"

assets/js/phoenix_live_view/dom_patch.js

@@ -15,6 +15,8 @@ import {
   PHX_STREAM_REF,
   PHX_VIEWPORT_TOP,
   PHX_VIEWPORT_BOTTOM,
+  PHX_PORTAL,
+  PHX_PORTAL_REF
 } from "./constants"
 
 import {
@@ -60,6 +62,7 @@ export default class DOMPatch {
     this.cidPatch = isCid(this.targetCID)
     this.pendingRemoves = []
     this.phxRemove = this.liveSocket.binding("remove")
+    this.portal = this.liveSocket.binding(PHX_PORTAL)
     this.targetContainer = this.isCIDPatch() ? this.targetCIDContainer(html) : container
     this.callbacks = {
       beforeadded: [], beforeupdated: [], beforephxChildAdded: [],
@@ -121,7 +124,18 @@ export default class DOMPatch {
         // tell morphdom how to add a child
         addChild: (parent, child) => {
           let {ref, streamAt} = this.getStreamInsert(child)
-          if(ref === undefined){ return parent.appendChild(child) }
+          if(ref === undefined){
+            // phx-portal optimization
+            if(child.getAttribute && child.getAttribute(PHX_PORTAL_REF) !== null){
+              const targetId = child.getAttribute(PHX_PORTAL_REF)
+              const portalTarget = DOM.byId(targetId)
+              child.removeAttribute(this.portal)
+              if(portalTarget.contains(child)){ return }
+              return portalTarget.appendChild(child)
+            }
+            // no special handling, we just append it to the parent
+            return parent.appendChild(child)
+          }
 
           this.setStreamRef(child, ref)
 
@@ -264,6 +278,24 @@ export default class DOMPatch {
           // input handling
           DOM.copyPrivates(toEl, fromEl)
 
+          // phx-portal handling
+          if(fromEl.hasAttribute(this.portal) || toEl.hasAttribute(this.portal)){
+            const targetId = toEl.getAttribute(this.portal)
+            const portalTarget = DOM.byId(targetId)
+            toEl.removeAttribute(this.portal)
+            toEl.setAttribute(PHX_PORTAL_REF, targetId)
+            const existing = document.getElementById(fromEl.id)
+            // if the child is already a descendent of the portal,
+            // keep it as is, to prevent unnecessary DOM operations
+            if(existing && portalTarget.contains(existing)){
+              return existing
+            } else {
+              // appendChild will move the element to the portal
+              portalTarget.appendChild(fromEl)
+              return fromEl
+            }
+          }
+
           // skip patching focused inputs unless focus is a select that has changed options
           if(isFocusedFormEl && fromEl.type !== "hidden" && !focusedSelectChanged){
             this.trackBefore("updated", fromEl, toEl)

test/e2e/support/portal.ex

@@ -0,0 +1,211 @@
+defmodule Phoenix.LiveViewTest.E2E.PortalLive do
+  use Phoenix.LiveView
+
+  alias Phoenix.LiveView.JS
+
+  def render("live.html", assigns) do
+    ~H"""
+    <meta name="csrf-token" content={Plug.CSRFProtection.get_csrf_token()} />
+    <script src="https://cdn.tailwindcss.com/3.4.3">
+    </script>
+    <script src="/assets/phoenix/phoenix.min.js">
+    </script>
+    <script type="module">
+      import {LiveSocket} from "/assets/phoenix_live_view/phoenix_live_view.esm.js"
+      let csrfToken = document.querySelector("meta[name='csrf-token']").getAttribute("content");
+      let liveSocket = new LiveSocket("/live", window.Phoenix.Socket, {params: {_csrf_token: csrfToken}})
+      liveSocket.connect()
+      window.liveSocket = liveSocket
+    </script>
+
+    <div id="portal-target"></div>
+
+    <main style="margin-left: 22rem; flex: 1; padding: 2rem;">
+      <%= @inner_content %>
+    </main>
+    """
+  end
+
+  @impl Phoenix.LiveView
+  def mount(params, _session, socket) do
+    case params do
+      %{"tick" => "false"} -> :ok
+      _ -> :timer.send_interval(1000, self(), :tick)
+    end
+
+    socket
+    |> assign(:param_current, nil)
+    |> assign(:count, 0)
+    |> then(&{:ok, &1, layout: {__MODULE__, :live}})
+  end
+
+  @impl Phoenix.LiveView
+  def handle_params(params, _uri, socket) do
+    param = Map.get(params, "param")
+
+    socket
+    |> assign(:param_current, param)
+    |> assign(:param_next, System.unique_integer())
+    |> then(&{:noreply, &1})
+  end
+
+  @impl Phoenix.LiveView
+  def handle_info(:tick, socket) do
+    {:noreply, assign(socket, :count, socket.assigns.count + 1)}
+  end
+
+  @impl Phoenix.LiveView
+  def handle_event("tick", _params, socket) do
+    {:noreply, assign(socket, :count, socket.assigns.count + 1)}
+  end
+
+  @impl Phoenix.LiveView
+  def render(assigns) do
+    ~H"""
+    <h1>Modal example</h1>
+
+    <p>Current param: <%= @param_current %></p>
+
+    <.button phx-click={JS.patch("/portal?param=#{@param_next}")}>Patch this LiveView</.button>
+
+    <.button phx-click={show_modal("my-modal")}>Open modal</.button>
+    <.button phx-click={show_modal("my-modal-2")}>Open second modal</.button>
+    <.button phx-click={JS.push("tick")}>Tick</.button>
+
+    <div id="portal-source" phx-portal="portal-target">
+      <.modal id="my-modal">
+        This is a modal.
+        <p>DOM patching works as expected: <%= @count %></p>
+        <.button phx-click={JS.patch("/portal?param=#{@param_next}")}>Patch this LiveView</.button>
+      </.modal>
+    </div>
+
+    <div id="portal-source-2" phx-portal="portal-target">
+      <.modal id="my-modal-2">
+        This is a second modal.
+      </.modal>
+    </div>
+    """
+  end
+
+  attr :type, :string, default: nil
+  attr :class, :string, default: nil
+  attr :rest, :global, include: ~w(disabled form name value)
+
+  slot :inner_block, required: true
+
+  def button(assigns) do
+    ~H"""
+    <button
+      type={@type}
+      class={[
+        "phx-submit-loading:opacity-75 rounded-lg bg-zinc-900 hover:bg-zinc-700 py-2 px-3",
+        "text-sm font-semibold leading-6 text-white active:text-white/80",
+        @class
+      ]}
+      {@rest}
+    >
+      <%= render_slot(@inner_block) %>
+    </button>
+    """
+  end
+
+  attr :id, :string, required: true
+  attr :show, :boolean, default: false
+  attr :on_cancel, JS, default: %JS{}
+  slot :inner_block, required: true
+
+  def modal(assigns) do
+    ~H"""
+    <div
+      id={@id}
+      phx-mounted={@show && show_modal(@id)}
+      phx-remove={hide_modal(@id)}
+      data-cancel={JS.exec(@on_cancel, "phx-remove")}
+      class="relative z-50 hidden"
+    >
+      <div id={"#{@id}-bg"} class="bg-zinc-50/90 fixed inset-0 transition-opacity" aria-hidden="true" />
+      <div
+        class="fixed inset-0 overflow-y-auto"
+        aria-labelledby={"#{@id}-title"}
+        aria-describedby={"#{@id}-description"}
+        role="dialog"
+        aria-modal="true"
+        tabindex="0"
+      >
+        <div class="flex min-h-full items-center justify-center">
+          <div class="w-full max-w-3xl p-4 sm:p-6 lg:py-8">
+            <.focus_wrap
+              id={"#{@id}-container"}
+              phx-window-keydown={JS.exec("data-cancel", to: "##{@id}")}
+              phx-key="escape"
+              phx-click-away={JS.exec("data-cancel", to: "##{@id}")}
+              class="shadow-zinc-700/10 ring-zinc-700/10 relative hidden rounded-2xl bg-white p-14 shadow-lg ring-1 transition"
+            >
+              <div class="absolute top-6 right-5">
+                <button
+                  phx-click={JS.exec("data-cancel", to: "##{@id}")}
+                  type="button"
+                  class="-m-3 flex-none p-3 opacity-20 hover:opacity-40"
+                  aria-label="close"
+                >
+                  x
+                </button>
+              </div>
+              <div id={"#{@id}-content"}>
+                <%= render_slot(@inner_block) %>
+              </div>
+            </.focus_wrap>
+          </div>
+        </div>
+      </div>
+    </div>
+    """
+  end
+
+  def show_modal(js \\ %JS{}, id) when is_binary(id) do
+    js
+    |> JS.show(to: "##{id}")
+    |> JS.show(
+      to: "##{id}-bg",
+      time: 300,
+      transition: {"transition-all ease-out duration-300", "opacity-0", "opacity-100"}
+    )
+    |> show("##{id}-container")
+    |> JS.add_class("overflow-hidden", to: "body")
+    |> JS.focus_first(to: "##{id}-content")
+  end
+
+  def hide_modal(js \\ %JS{}, id) do
+    js
+    |> JS.hide(
+      to: "##{id}-bg",
+      transition: {"transition-all ease-in duration-200", "opacity-100", "opacity-0"}
+    )
+    |> hide("##{id}-container")
+    |> JS.hide(to: "##{id}", transition: {"block", "block", "hidden"})
+    |> JS.remove_class("overflow-hidden", to: "body")
+    |> JS.pop_focus()
+  end
+
+  def show(js \\ %JS{}, selector) do
+    JS.show(js,
+      to: selector,
+      time: 300,
+      transition:
+        {"transition-all ease-out duration-300",
+         "opacity-0 translate-y-4 sm:translate-y-0 sm:scale-95",
+         "opacity-100 translate-y-0 sm:scale-100"}
+    )
+  end
+
+  def hide(js \\ %JS{}, selector) do
+    JS.hide(js,
+      to: selector,
+      time: 200,
+      transition:
+        {"transition-all ease-in duration-200", "opacity-100 translate-y-0 sm:scale-100",
+         "opacity-0 translate-y-4 sm:translate-y-0 sm:scale-95"}
+    )
+  end
+end

test/e2e/test_helper.exs

@@ -132,6 +132,7 @@ defmodule Phoenix.LiveViewTest.E2E.Router do
       live "/form/stream", E2E.FormStreamLive
       live "/js", E2E.JsLive
       live "/select", E2E.SelectLive
+      live "/portal", E2E.PortalLive
     end
 
     scope "/issues", Phoenix.LiveViewTest.E2E do

test/e2e/tests/portal.spec.js

@@ -0,0 +1,19 @@
+const { test, expect } = require("../test-fixtures");
+const { syncLV, evalLV } = require("../utils");
+
+test("renders modal inside portal location", async ({ page }) => {
+  await page.goto("/portal?tick=false");
+  await syncLV(page);
+
+  await expect(page.locator("#my-modal")).toHaveCount(1);
+  await expect(page.locator("#my-modal-content")).not.toBeVisible();
+  // no modal inside the main element (rendered in the layout)
+  await expect(page.locator("main #my-modal")).toHaveCount(0);
+
+  await page.getByRole("button", { name: "Open modal" }).click();
+  await expect(page.locator("#my-modal-content")).toBeVisible();
+
+  await expect(page.locator("#my-modal-content")).toContainText("DOM patching works as expected: 0");
+  await evalLV(page, `send(self(), :tick)`);
+  await expect(page.locator("#my-modal-content")).toContainText("DOM patching works as expected: 1");
+});