Change button copy on theme preview

This commit makes the dark mode preview feel a little more interactive
and it also pulls some duplicated code into one file so that people like
me aren't stumped when they are looking at the wrong page!

assets/js/dark-mode-preview.js

+document.addEventListener("DOMContentLoaded", function(){
+
+  const toggleDarkMode = document.querySelector('.js-toggle-dark-mode')
+  const cssFile = document.querySelector('[rel="stylesheet"]')
+  const originalCssRef = cssFile.getAttribute('href')
+  const darkModeCssRef = originalCssRef.replace('just-the-docs.css', 'dark-mode-preview.css')
+  const buttonCopy = ['Return to the light side', 'Preview dark color scheme']
+  const updateButtonText = function(toggleDarkMode) {
+    toggleDarkMode.textContent === buttonCopy[0] ?
+      toggleDarkMode.textContent = buttonCopy[1] :
+      toggleDarkMode.textContent = buttonCopy[0]
+  }
+
+  addEvent(toggleDarkMode, 'click', function(){
+    if (cssFile.getAttribute('href') === originalCssRef) {
+      cssFile.setAttribute('href', darkModeCssRef)
+      updateButtonText(toggleDarkMode)
+    } else {
+      cssFile.setAttribute('href', originalCssRef)
+      updateButtonText(toggleDarkMode)
+    }
+  })
+})
\ No newline at end of file

docs/configuration.md

@@ -46,20 +46,7 @@ color_scheme: "dark"
 ```
 <button class="btn js-toggle-dark-mode">Preview dark color scheme</button>
 
-<script>
-const toggleDarkMode = document.querySelector('.js-toggle-dark-mode')
-const cssFile = document.querySelector('[rel="stylesheet"]')
-const originalCssRef = cssFile.getAttribute('href')
-const darkModeCssRef = originalCssRef.replace('just-the-docs.css', 'dark-mode-preview.css')
-
-addEvent(toggleDarkMode, 'click', function(){
-  if (cssFile.getAttribute('href') === originalCssRef) {
-    cssFile.setAttribute('href', darkModeCssRef)
-  } else {
-    cssFile.setAttribute('href', originalCssRef)
-  }
-})
-</script>
+<script type="text/javascript" src="{{ "/assets/js/dark-mode-preview.js" | absolute_url }}"></script>
 
 See [Customization]({{ site.baseurl }}{% link docs/customization.md %}) for more information.
 

docs/customization.md

@@ -34,20 +34,7 @@ color_scheme: "dark"
 ```
 <button class="btn js-toggle-dark-mode">Preview dark color scheme</button>
 
-<script>
-const toggleDarkMode = document.querySelector('.js-toggle-dark-mode')
-const cssFile = document.querySelector('[rel="stylesheet"]')
-const originalCssRef = cssFile.getAttribute('href')
-const darkModeCssRef = originalCssRef.replace('just-the-docs.css', 'dark-mode-preview.css')
-
-addEvent(toggleDarkMode, 'click', function(){
-  if (cssFile.getAttribute('href') === originalCssRef) {
-    cssFile.setAttribute('href', darkModeCssRef)
-  } else {
-    cssFile.setAttribute('href', originalCssRef)
-  }
-})
-</script>
+<script type="text/javascript" src="{{ "/assets/js/dark-mode-preview.js" | absolute_url }}"></script>
 
 ## Specific visual customization