Add code copy button to all code fields in the blog (#81)

assets/js/code-copy.js

@@ -0,0 +1,56 @@
+/**
+ * Utils
+ */
+
+// Add code-copy buttons using progressive enhancement
+// © 2019. Tom Spencer
+// https://www.fiznool.com/blog/2018/09/14/adding-click-to-copy-buttons-to-a-hugo-powered-blog/
+(function() {
+  'use strict';
+
+  if(!document.queryCommandSupported('copy')) {
+    return;
+  }
+
+  function flashCopyMessage(el, msg) {
+    el.textContent = msg;
+    setTimeout(function() {
+      el.textContent = "Copy";
+    }, 1000);
+  }
+
+  function selectText(node) {
+    var selection = window.getSelection();
+    var range = document.createRange();
+    range.selectNodeContents(node);
+    selection.removeAllRanges();
+    selection.addRange(range);
+    return selection;
+  }
+
+  function addCopyButton(containerEl) {
+    var copyBtn = document.createElement("button");
+    copyBtn.className = "highlight-copy-btn";
+    copyBtn.textContent = "Copy";
+
+    var codeEl = containerEl.firstElementChild;
+    copyBtn.addEventListener('click', function() {
+      try {
+        var selection = selectText(codeEl);
+        document.execCommand('copy');
+        selection.removeAllRanges();
+
+        flashCopyMessage(copyBtn, 'Copied!')
+      } catch(e) {
+        console && console.log(e);
+        flashCopyMessage(copyBtn, 'Failed :\'(')
+      }
+    });
+
+    containerEl.appendChild(copyBtn);
+  }
+
+  // Add copy button to code blocks
+  var highlightBlocks = document.getElementsByClassName('highlight');
+  Array.prototype.forEach.call(highlightBlocks, addCopyButton);
+})();