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fix(web): prevent dark theme navigation flash #219

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Merged
ccarvalho-eng merged 1 commit into from
Sep 5, 2026
Merged

fix(web): prevent dark theme navigation flash #219

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11 changes: 11 additions & 0 deletions assets/js/app.js
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,10 @@ const AutoDismissFlash = {

// Theme switching logic
function setTheme(theme) {
if (!['system', 'light', 'dark'].includes(theme)) {
theme = 'system'
}

localStorage.setItem('theme', theme)

let appliedTheme = theme
Expand Down Expand Up @@ -79,6 +83,13 @@ window.addEventListener('phx:set-theme', (e) => {
}
})

// Keep the theme in sync when another browser window changes it.
window.addEventListener('storage', (e) => {
if (e.key === 'theme') {
setTheme(e.newValue || 'system')
}
})

// Watch for system theme changes
window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', (e) => {
const currentTheme = localStorage.getItem('theme')
Expand Down
4 changes: 2 additions & 2 deletions lib/aludel/web/components/layouts.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -201,9 +201,9 @@ defmodule Aludel.Web.Layouts do
assigns = assign(assigns, :active, active)

~H"""
<a href={@href} class={"aludel-nav-link #{@active}"}>
<.link navigate={@href} class={"aludel-nav-link #{@active}"}>
{render_slot(@inner_block)}
</a>
</.link>
"""
end
end
33 changes: 16 additions & 17 deletions lib/aludel/web/components/layouts/root.html.heex
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Expand Up @@ -10,28 +10,27 @@
{assigns[:page_title] || "Dashboard"}
</.live_title>
<link rel="icon" type="image/svg+xml" href="/favicon.svg" />
<link rel="stylesheet" href={asset_path(@conn, :css)} />
<script defer src={asset_path(@conn, :js)}>
</script>
<script>
(() => {
const setTheme = (theme) => {
if (theme === "system") {
localStorage.removeItem("phx:theme");
document.documentElement.removeAttribute("data-theme");
} else {
localStorage.setItem("phx:theme", theme);
document.documentElement.setAttribute("data-theme", theme);
}
};
if (!document.documentElement.hasAttribute("data-theme")) {
setTheme(localStorage.getItem("phx:theme") || "system");
let savedTheme = "system";

try {
savedTheme = localStorage.getItem("theme") || "system";
} catch (_error) {
// Storage can be unavailable in privacy-restricted browsing contexts.
}
window.addEventListener("storage", (e) => e.key === "phx:theme" && setTheme(e.newValue || "system"));

window.addEventListener("phx:set-theme", (e) => setTheme(e.target.dataset.phxTheme));

const theme = ["system", "light", "dark"].includes(savedTheme) ? savedTheme : "system";
const appliedTheme = theme === "system"
? (window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light")
: theme;

document.documentElement.setAttribute("data-theme", appliedTheme);
})();
</script>
<link rel="stylesheet" href={asset_path(@conn, :css)} />
<script defer src={asset_path(@conn, :js)}>
</script>
</head>
<body>
{@inner_content}
Expand Down
8 changes: 8 additions & 0 deletions priv/static/app.js
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Original file line number Diff line number Diff line change
Expand Up @@ -22227,6 +22227,9 @@ removing illegal node: "${("outerHTML" in childNode && childNode.outerHTML || ch
}
};
function setTheme(theme) {
if (!["system", "light", "dark"].includes(theme)) {
theme = "system";
}
localStorage.setItem("theme", theme);
let appliedTheme = theme;
if (theme === "system") {
Expand All @@ -22251,6 +22254,11 @@ removing illegal node: "${("outerHTML" in childNode && childNode.outerHTML || ch
setTheme(theme);
}
});
window.addEventListener("storage", (e) => {
if (e.key === "theme") {
setTheme(e.newValue || "system");
}
});
window.matchMedia("(prefers-color-scheme: dark)").addEventListener("change", (e) => {
const currentTheme = localStorage.getItem("theme");
if (currentTheme === "system" || !currentTheme) {
Expand Down
20 changes: 20 additions & 0 deletions test/aludel_web/live/dashboard_live_test.exs
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Expand Up @@ -13,6 +13,26 @@ defmodule Aludel.Web.DashboardLiveTest do
assert render(view) =~ "Dashboard"
end

test "applies the saved theme before loading styles", %{conn: conn} do
html = conn |> get("/") |> html_response(200)

theme_script_position =
html
|> :binary.match(~s|localStorage.getItem("theme")|)
|> elem(0)

stylesheet_position =
html
|> :binary.match(~s(rel="stylesheet"))
|> elem(0)

assert theme_script_position < stylesheet_position
assert html =~ ~s|document.documentElement.setAttribute("data-theme", appliedTheme)|
refute html =~ "phx:theme"
assert html =~ ~s|href="/prompts"|
assert html =~ ~s|data-phx-link="redirect"|
end

test "shows recent runs", %{conn: conn} do
_run = run_fixture(%{name: "Recent Test Run"})

Expand Down
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