Add copy code block button support to docs (#157)

docs/siteConfig.js

@@ -0,0 +1,6 @@
+scripts: [
+    'https://buttons.github.io/buttons.js',
+    'https://cdnjs.cloudflare.com/ajax/libs/clipboard.js/2.0.0/clipboard.min.js',
+    '/js/code-block-buttons.js',
+  ],
+  stylesheets: ['/css/code-block-buttons.css']

docs/static/css/code-block-buttons.css

@@ -0,0 +1,39 @@
+/* "Copy" code block button */
+pre {
+    position: relative;
+  }
+  
+  pre .btnIcon {
+    position: absolute;
+    top: 4px;
+    z-index: 2;
+    cursor: pointer;
+    border: 1px solid transparent;
+    padding: 0;
+    color: #fff;
+    background-color: transparent;
+    height: 30px;
+    transition: all .25s ease-out;
+  }
+  
+  pre .btnIcon:hover {
+    text-decoration: none;
+  }
+  
+  .btnIcon__body {
+    align-items: center;
+    display: flex;
+  }
+  
+  .btnIcon svg {
+    fill: currentColor;
+    margin-right: .4em;
+  }
+  
+  .btnIcon__label {
+    font-size: 11px;
+  }
+  
+  .btnClipboard {
+    right: 10px;
+  }

docs/static/js/code-block-buttons.js

@@ -0,0 +1,48 @@
+// Turn off ESLint for this file because it's sent down to users as-is.
+/* eslint-disable */
+window.addEventListener('load', function() {
+    function button(label, ariaLabel, icon, className) {
+      const btn = document.createElement('button');
+      btn.classList.add('btnIcon', className);
+      btn.setAttribute('type', 'button');
+      btn.setAttribute('aria-label', ariaLabel);
+      btn.innerHTML =
+        '<div class="btnIcon__body">' +
+        icon +
+        '<strong class="btnIcon__label">' +
+        label +
+        '</strong>' +
+        '</div>';
+      return btn;
+    }
+  
+    function addButtons(codeBlockSelector, btn) {
+      document.querySelectorAll(codeBlockSelector).forEach(function(code) {
+        code.parentNode.appendChild(btn.cloneNode(true));
+      });
+    }
+  
+    const copyIcon =
+      '<svg width="12" height="12" viewBox="340 364 14 15" xmlns="http://www.w3.org/2000/svg"><path fill="currentColor" d="M342 375.974h4v.998h-4v-.998zm5-5.987h-5v.998h5v-.998zm2 2.994v-1.995l-3 2.993 3 2.994v-1.996h5v-1.995h-5zm-4.5-.997H342v.998h2.5v-.997zm-2.5 2.993h2.5v-.998H342v.998zm9 .998h1v1.996c-.016.28-.11.514-.297.702-.187.187-.422.28-.703.296h-10c-.547 0-1-.452-1-.998v-10.976c0-.546.453-.998 1-.998h3c0-1.107.89-1.996 2-1.996 1.11 0 2 .89 2 1.996h3c.547 0 1 .452 1 .998v4.99h-1v-2.995h-10v8.98h10v-1.996zm-9-7.983h8c0-.544-.453-.996-1-.996h-1c-.547 0-1-.453-1-.998 0-.546-.453-.998-1-.998-.547 0-1 .452-1 .998 0 .545-.453.998-1 .998h-1c-.547 0-1 .452-1 .997z" fill-rule="evenodd"/></svg>';
+  
+    addButtons(
+      '.hljs',
+      button('Copy', 'Copy code to clipboard', copyIcon, 'btnClipboard'),
+    );
+  
+    const clipboard = new ClipboardJS('.btnClipboard', {
+      target: function(trigger) {
+        return trigger.parentNode.querySelector('code');
+      },
+    });
+  
+    clipboard.on('success', function(event) {
+      event.clearSelection();
+      const textEl = event.trigger.querySelector('.btnIcon__label');
+      textEl.textContent = 'Copied';
+      setTimeout(function() {
+        textEl.textContent = 'Copy';
+      }, 2000);
+    });
+  });
+