Support default title attribute

assets/js/phoenix_live_view/dom.js

@@ -213,8 +213,12 @@ let DOM = {
   putTitle(str){
     let titleEl = document.querySelector("title")
     if(titleEl){
-      let {prefix, suffix} = titleEl.dataset
-      document.title = `${prefix || ""}${str}${suffix || ""}`
+      let {prefix, suffix, default: defaultTitle} = titleEl.dataset
+      let isEmpty = typeof(str) !== "string" || str.trim() === ""
+      if(isEmpty && typeof(defaultTitle) !== "string"){ return }
+
+      let inner = isEmpty ? defaultTitle : str
+      document.title = `${prefix || ""}${inner || ""}${suffix || ""}`
     } else {
       document.title = str
     }

assets/js/phoenix_live_view/view.js

@@ -302,7 +302,7 @@ export default class View {
     this.log(type, () => ["", clone(rawDiff)])
     let {diff, reply, events, title} = Rendered.extract(rawDiff)
     callback({diff, reply, events})
-    if(typeof title === "string"){ window.requestAnimationFrame(() => DOM.putTitle(title)) }
+    if(typeof title === "string" || type == "mount"){ window.requestAnimationFrame(() => DOM.putTitle(title)) }
   }
 
   onJoin(resp){

assets/test/dom_test.js

@@ -118,6 +118,18 @@ describe("DOM", () => {
       DOM.putTitle("My Title")
       expect(document.title).toBe("PRE My Title POST")
     })
+
+    test("with default", () => {
+      appendTitle({default: "DEFAULT", prefix: "PRE ", suffix: " POST"})
+      DOM.putTitle(null)
+      expect(document.title).toBe("PRE DEFAULT POST")
+
+      DOM.putTitle(undefined)
+      expect(document.title).toBe("PRE DEFAULT POST")
+
+      DOM.putTitle("")
+      expect(document.title).toBe("PRE DEFAULT POST")
+    })
   })
 
   describe("findExistingParentCIDs", () => {

assets/test/test_helpers.js

@@ -1,11 +1,18 @@
 import View from "phoenix_live_view/view"
 import {version as liveview_version} from "../package.json"
 
-export let appendTitle = opts => {
+export let appendTitle = (opts, innerHTML) => {
+  Array.from(document.head.querySelectorAll("title")).forEach(el => el.remove())
   let title = document.createElement("title")
-  let {prefix, suffix} = opts
+  let {prefix, suffix, default: defaultTitle} = opts
   if(prefix){ title.setAttribute("data-prefix", prefix) }
   if(suffix){ title.setAttribute("data-suffix", suffix) }
+  if(defaultTitle){
+    title.setAttribute("data-default", defaultTitle)
+  } else {
+    title.removeAttribute("data-default")
+  }
+  if(innerHTML){ title.innerHTML = innerHTML }
   document.head.appendChild(title)
 }
 
@@ -78,5 +85,3 @@ export function liveViewDOM(content){
   document.body.appendChild(div)
   return div
 }
-
-

assets/test/view_test.js

@@ -12,7 +12,7 @@ import {
   PHX_HAS_FOCUSED
 } from "phoenix_live_view/constants"
 
-import {tag, simulateJoinedView, stubChannel, rootContainer, liveViewDOM, simulateVisibility} from "./test_helpers"
+import {tag, simulateJoinedView, stubChannel, rootContainer, liveViewDOM, simulateVisibility, appendTitle} from "./test_helpers"
 
 let simulateUsedInput = (input) => {
   DOM.putPrivate(input, PHX_HAS_FOCUSED, true)
@@ -44,9 +44,10 @@ describe("View + DOM", function(){
     expect(view.rendered.get()).toEqual(updateDiff)
   })
 
-  test("applyDiff can set title to falsy values", async () => {
-    document.title = "Foo"
+  test("applyDiff with empty title uses default if present", async () => {
+    appendTitle({}, "Foo")
 
+    let titleEl = document.querySelector("title")
     let liveSocket = new LiveSocket("/live", Socket)
     let el = liveViewDOM()
     let updateDiff = {
@@ -56,13 +57,17 @@ describe("View + DOM", function(){
     }
 
     let view = simulateJoinedView(el, liveSocket)
-    view.applyDiff("update", updateDiff, ({diff, events}) => view.update(diff, events))
+    view.applyDiff("mount", updateDiff, ({diff, events}) => view.update(diff, events))
 
     expect(view.el.firstChild.tagName).toBe("H2")
     expect(view.rendered.get()).toEqual(updateDiff)
 
     await new Promise(requestAnimationFrame)
-    expect(document.title).toBe("")
+    expect(document.title).toBe("Foo")
+    titleEl.setAttribute("data-default", "DEFAULT")
+    view.applyDiff("mount", updateDiff, ({diff, events}) => view.update(diff, events))
+    await new Promise(requestAnimationFrame)
+    expect(document.title).toBe("DEFAULT")
   })
 
   test("pushWithReply", function(){

lib/phoenix_component.ex

@@ -2084,14 +2084,14 @@ defmodule Phoenix.Component do
   ## Examples
 
   ```heex
-  <.live_title prefix="MyApp – ">
-    <%= assigns[:page_title] || "Welcome" %>
+  <.live_title default="Welcome" prefix="MyApp – ">
+    <%= assigns[:page_title] %>
   </.live_title>
   ```
 
   ```heex
-  <.live_title suffix="- MyApp">
-    <%= assigns[:page_title] || "Welcome" %>
+  <.live_title default="Welcome" suffix="- MyApp">
+    <%= assigns[:page_title] %>
   </.live_title>
   ```
   """
@@ -2101,15 +2101,33 @@ defmodule Phoenix.Component do
     doc: "A prefix added before the content of `inner_block`."
   )
 
+  attr.(:default, :string,
+    default: nil,
+    doc: "The default title to use if the inner block is empty on regular or connected mounts."
+  )
+
   attr.(:suffix, :string, default: nil, doc: "A suffix added after the content of `inner_block`.")
   slot.(:inner_block, required: true, doc: "Content rendered inside the `title` tag.")
 
   def live_title(assigns) do
     ~H"""
-    <title data-prefix={@prefix} data-suffix={@suffix} phx-no-format><%= @prefix %><%= render_slot(@inner_block) %><%= @suffix %></title>
+    <title data-prefix={@prefix} data-default={@default} data-suffix={@suffix} phx-no-format><%= @prefix %><%= render_present(render_slot(@inner_block), @default) %><%= @suffix %></title>
     """
   end
 
+  defp render_present(rendered_block, default) do
+    block_str =
+      rendered_block
+      |> Phoenix.HTML.html_escape()
+      |> Phoenix.HTML.safe_to_string()
+
+    if String.trim(block_str) == "" do
+      default
+    else
+      rendered_block
+    end
+  end
+
   @doc ~S'''
   Renders a form.
 

test/phoenix_component/components_test.exs

@@ -185,6 +185,25 @@ defmodule Phoenix.LiveView.ComponentsTest do
       assert t2h(~H|<.live_title>My Title</.live_title>|) ==
                ~X|<title>My Title</title>|
     end
+
+    test "default with blank inner block" do
+      assigns = %{
+        val: """
+
+
+        """
+      }
+
+      assert t2h(~H|<.live_title default="DEFAULT" phx-no-format>   <%= @val %>   </.live_title>|) ==
+               ~X|<title data-default="DEFAULT">DEFAULT</title>|
+    end
+
+    test "default with present inner block" do
+      assigns = %{val: "My Title"}
+
+      assert t2h(~H|<.live_title default="DEFAULT" phx-no-format>   <%= @val %>   </.live_title>|) ==
+               ~X|<title data-default="DEFAULT">   My Title   </title>|
+    end
   end
 
   describe "dynamic_tag/1" do