refactor: update toggle theme function for better structure and a11y

satnaing · satnaing · commit 0eeed8e87078 · 2022-11-26T23:43:27.000+06:30
Move theme switch js codes in Layout.astro file to external js file (toggle-theme.js). Update
.prettierignore to exclude the new toggle-theme.js file.  Update base.css for new data-theme
attribute.
diff --git a/.prettierignore b/.prettierignore
@@ -3,6 +3,7 @@
 
 # Except these files & folders
 !/src
+!/public
 !/.github
 !tsconfig.json
 !astro.config.mjs
diff --git a/public/toggle-theme.js b/public/toggle-theme.js
@@ -0,0 +1,52 @@
+const primaryColorScheme = ""; // "light" | "dark"
+
+// Get theme data from local storage
+const currentTheme = localStorage.getItem("theme");
+
+function getPreferTheme() {
+  // return theme value in local storage if it is set
+  if (currentTheme) return currentTheme;
+
+  // return primary color scheme if it is set
+  if (primaryColorScheme) return primaryColorScheme;
+
+  // return user device's prefer color scheme
+  return window.matchMedia("(prefers-color-scheme: dark)").matches
+    ? "dark"
+    : "light";
+}
+
+let themeValue = getPreferTheme();
+
+function setPreference() {
+  localStorage.setItem("theme", themeValue);
+  reflectPreference();
+}
+
+function reflectPreference() {
+  document.firstElementChild.setAttribute("data-theme", themeValue);
+
+  document.querySelector("#theme-btn")?.setAttribute("aria-label", themeValue);
+}
+
+// set early so no page flashes / CSS is made aware
+reflectPreference();
+
+window.onload = () => {
+  // set on load so screen readers can get the latest value on the button
+  reflectPreference();
+
+  // now this script can find and listen for clicks on the control
+  document.querySelector("#theme-btn").addEventListener("click", () => {
+    themeValue = themeValue === "light" ? "dark" : "light";
+    setPreference();
+  });
+};
+
+// sync with system changes
+window
+  .matchMedia("(prefers-color-scheme: dark)")
+  .addEventListener("change", ({ matches: isDark }) => {
+    themeValue = isDark ? "dark" : "light";
+    setPreference();
+  });
diff --git a/src/layouts/Layout.astro b/src/layouts/Layout.astro
@@ -61,45 +61,7 @@ const socialImageURL = new URL(
       onload="this.onload=null;this.rel='stylesheet'"
     />
 
-    <script is:inline>
-      const primaryColorScheme = "none"; // "light" | "dark" | "none"
-
-      const darkModeMediaQuery = window.matchMedia(
-        "(prefers-color-scheme: dark)"
-      ).matches;
-
-      // Get theme data from local storage
-      const currentTheme = localStorage.getItem("theme");
-
-      let theme;
-
-      // Set theme to 'theme-dark' if currentTheme is 'dark'
-      if (currentTheme) {
-        theme = currentTheme === "dark" ? "theme-dark" : "";
-      } else {
-        // If primary color scheme is dark
-        // or primary color scheme is not set and prefers-color-scheme is dark
-        // choose dark mode
-        if (
-          primaryColorScheme === "dark" ||
-          (primaryColorScheme === "none" && darkModeMediaQuery)
-        ) {
-          theme = "theme-dark";
-        }
-        // If primary color scheme is light
-        // choose light mode
-        else if (primaryColorScheme === "light") {
-          theme = "";
-        }
-        // fallback to prefers-color-scheme
-        else {
-          theme = darkModeMediaQuery ? "theme-dark" : "";
-        }
-      }
-
-      // Put dark class on html tag to enable dark mode
-      document.querySelector("html").className = theme;
-    </script>
+    <script is:inline src="/toggle-theme.js"></script>
   </head>
   <body>
     <slot />
diff --git a/src/styles/base.css b/src/styles/base.css
@@ -3,15 +3,16 @@
 @tailwind utilities;
 
 @layer base {
-  :root {
+  :root,
+  html[data-theme="light"] {
     --color-fill: 251, 254, 251;
     --color-text-base: 40, 39, 40;
     --color-accent: 0, 108, 172;
     --color-card: 230, 230, 230;
     --color-card-muted: 205, 205, 205;
     --color-border: 236, 233, 233;
   }
-  .theme-dark {
+  html[data-theme="dark"] {
     --color-fill: 47, 55, 65;
     --color-text-base: 230, 230, 230;
     --color-accent: 26, 217, 217;
@@ -20,11 +21,11 @@
     --color-border: 59, 70, 85;
   }
   #sun-svg,
-  .theme-dark #moon-svg {
+  html[data-theme="dark"] #moon-svg {
     display: none;
   }
   #moon-svg,
-  .theme-dark #sun-svg {
+  html[data-theme="dark"] #sun-svg {
     display: block;
   }
   body {
@@ -36,7 +37,8 @@
     @apply max-w-3xl mx-auto px-4;
   }
   a {
-    @apply outline-offset-1 outline-skin-fill outline-2 focus-visible:outline-dashed focus-visible:no-underline;
+    @apply outline-offset-1 outline-skin-fill outline-2 
+    focus-visible:outline-dashed focus-visible:no-underline;
   }
   svg {
     @apply w-6 h-6 inline-block fill-skin-base group-hover:fill-skin-accent;
