Add "copy to clipboard" button for code blocks (#2812)

* Add copy-to-clipboard button and JS

* Ignore line numbers if present

* Rewrite heading permalink code to use vanilla JS

* README: Add credits to zenorocha/clipboard.js (MIT License)

@iBug really wants a place here in the Credits section :P

* Add .no-copy for hiding the button, update docs

* Add td.rouge-code to selectors

* Fix navigator.clipboard branch

* Add screenreader text for copy button

* Restore focus to the button after copying

* Add site-wide enable switch

assets/js/_main.js

@@ -2,18 +2,18 @@
    jQuery plugin settings and other scripts
    ========================================================================== */
 
-$(function() {
+$(document).ready(function () {
   // FitVids init
   $("#main").fitVids();
 
   // Follow menu drop down
-  $(".author__urls-wrapper").find("button").on("click", function() {
+  $(".author__urls-wrapper button").on("click", function () {
     $(".author__urls").toggleClass("is--visible");
     $(".author__urls-wrapper").find("button").toggleClass("open");
   });
 
   // Close search screen with Esc key
-  $(document).keyup(function(e) {
+  $(document).keyup(function (e) {
     if (e.keyCode === 27) {
       if ($(".initial-content").hasClass("is--hidden")) {
         $(".search-content").toggleClass("is--visible");
@@ -23,12 +23,12 @@ $(function() {
   });
 
   // Search toggle
-  $(".search__toggle").on("click", function() {
+  $(".search__toggle").on("click", function () {
     $(".search-content").toggleClass("is--visible");
     $(".initial-content").toggleClass("is--hidden");
     // set focus on input
-    setTimeout(function() {
-      $(".search-content").find("input").focus();
+    setTimeout(function () {
+      $(".search-content input").focus();
     }, 400);
   });
 
@@ -37,11 +37,11 @@ $(function() {
     offset: 20,
     speed: 400,
     speedAsDuration: true,
-    durationMax: 500
+    durationMax: 500,
   });
 
   // Gumshoe scroll spy init
-  if($("nav.toc").length > 0) {
+  if ($("nav.toc").length > 0) {
     var spy = new Gumshoe("nav.toc a", {
       // Active classes
       navClass: "active", // applied to the nav list item
@@ -56,7 +56,7 @@ $(function() {
       reflow: true, // if true, listen for reflows
 
       // Event support
-      events: true // if true, emit custom events
+      events: true, // if true, emit custom events
     });
   }
 
@@ -95,38 +95,120 @@ $(function() {
     gallery: {
       enabled: true,
       navigateByImgClick: true,
-      preload: [0, 1] // Will preload 0 - before current, and 1 after the current image
+      preload: [0, 1], // Will preload 0 - before current, and 1 after the current image
     },
     image: {
-      tError: '<a href="%url%">Image #%curr%</a> could not be loaded.'
+      tError: '<a href="%url%">Image #%curr%</a> could not be loaded.',
     },
     removalDelay: 500, // Delay in milliseconds before popup is removed
     // Class that is added to body when popup is open.
     // make it unique to apply your CSS animations just to this exact popup
     mainClass: "mfp-zoom-in",
     callbacks: {
-      beforeOpen: function() {
+      beforeOpen: function () {
         // just a hack that adds mfp-anim class to markup
         this.st.image.markup = this.st.image.markup.replace(
           "mfp-figure",
           "mfp-figure mfp-with-anim"
         );
-      }
+      },
     },
     closeOnContentClick: true,
-    midClick: true // allow opening popup on middle mouse click. Always set it to true if you don't provide alternative source.
+    midClick: true, // allow opening popup on middle mouse click. Always set it to true if you don't provide alternative source.
   });
 
   // Add anchors for headings
-  $('.page__content').find('h1, h2, h3, h4, h5, h6').each(function() {
-    var id = $(this).attr('id');
-    if (id) {
-      var anchor = document.createElement("a");
-      anchor.className = 'header-link';
-      anchor.href = '#' + id;
-      anchor.innerHTML = '<span class=\"sr-only\">Permalink</span><i class=\"fas fa-link\"></i>';
-      anchor.title = "Permalink";
-      $(this).append(anchor);
+  document
+    .querySelector(".page__content")
+    .querySelectorAll("h1, h2, h3, h4, h5, h6")
+    .forEach(function (element) {
+      var id = element.getAttribute("id");
+      if (id) {
+        var anchor = document.createElement("a");
+        anchor.className = "header-link";
+        anchor.href = "#" + id;
+        anchor.innerHTML =
+          '<span class="sr-only">Permalink</span><i class="fas fa-link"></i>';
+        anchor.title = "Permalink";
+        element.appendChild(anchor);
+      }
+    });
+
+  // Add copy button for <pre> blocks
+  var copyText = function (text) {
+    if (document.queryCommandEnabled("copy") && navigator.clipboard) {
+      navigator.clipboard.writeText(text).then(
+        () => true,
+        () => console.error("Failed to copy text to clipboard: " + text)
+      );
+      return true;
+    } else {
+      var isRTL = document.documentElement.getAttribute("dir") === "rtl";
+
+      var textarea = document.createElement("textarea");
+      textarea.className = "clipboard-helper";
+      textarea.style[isRTL ? "right" : "left"] = "-9999px";
+      // Move element to the same position vertically
+      var yPosition = window.pageYOffset || document.documentElement.scrollTop;
+      textarea.style.top = yPosition + "px";
+
+      textarea.setAttribute("readonly", "");
+      textarea.value = text;
+      document.body.appendChild(textarea);
+
+      var success = true;
+      try {
+        textarea.select();
+        success = document.execCommand("copy");
+      } catch (e) {
+        success = false;
+      }
+      textarea.parentNode.removeChild(textarea);
+      return success;
     }
-  });
+  };
+
+  var copyButtonEventListener = function (event) {
+    var thisButton = event.target;
+
+    // Locate the <code> element
+    var codeBlock = thisButton.nextElementSibling;
+    while (codeBlock && codeBlock.tagName.toLowerCase() !== "code") {
+      codeBlock = codeBlock.nextElementSibling;
+    }
+    if (!codeBlock) {
+      // No <code> found - wtf?
+      console.warn(thisButton);
+      throw new Error("No code block found for this button.");
+    }
+
+    // Skip line numbers if present (i.e. {% highlight lineno %})
+    var realCodeBlock = codeBlock.querySelector("td.code, td.rouge-code");
+    if (realCodeBlock) {
+      codeBlock = realCodeBlock;
+    }
+    var result = copyText(codeBlock.innerText);
+    // Restore the focus to the button
+    thisButton.focus();
+    return result;
+  };
+
+  if (window.enable_copy_code_button) {
+    document
+      .querySelectorAll(".page__content pre > code")
+      .forEach(function (element, index, parentList) {
+        // Locate the <pre> element
+        var container = element.parentElement;
+        // Sanity check - don't add an extra button if there's already one
+        if (container.firstElementChild.tagName.toLowerCase() !== "code") {
+          return;
+        }
+        var copyButton = document.createElement("button");
+        copyButton.title = "Copy to clipboard";
+        copyButton.className = "clipboard-copy-button";
+        copyButton.innerHTML = '<span class="sr-only">Copy code</span><i class="far fa-copy"></i>';
+        copyButton.addEventListener("click", copyButtonEventListener);
+        container.prepend(copyButton);
+      });
+  }
 });