Issue#946 open links in new tab (#1009)

I added two helper functions that are called inside the editor's `render` method.

`openLinksInNewTab` prevents the default click event on external links (all anchors with an `href` attribute that starts with `http`) and opens them in a new tab.

While I was at it, I stumbled upon the issue that relative links (like `<a href="#someanchor">`) also didn't work. I didn't find a ticket for that so I thought it would make sense to fix in the scope of this ticket.

`scrollToAnchors` prevents the default click event on relative links and scrolls the targeted anchor into view.

I hope that the code structure adheres to your quality standards.

js/editor-libs/mce-utils.js

@@ -37,6 +37,19 @@ module.exports = {
 
         return tmpElem.style[property] !== undefined;
     },
+    /**
+     * Interrupts the default click event on external links inside
+     * the shadow dom and opens them in a new tab instead
+     * @param {Array} externalLinks - all external links inside the shadow dom
+     */
+    openLinksInNewTab: function(externalLinks) {
+        externalLinks.forEach(function(externalLink) {
+            externalLink.addEventListener('click', function(event) {
+                event.preventDefault();
+                window.open(externalLink.href);
+            });
+        });
+    },
     /**
      * Posts a name to set as a mark to Kuma for
      * processing and beaconing to GA
@@ -45,6 +58,20 @@ module.exports = {
     postToKuma: function(perf) {
         window.parent.postMessage(perf, 'https://developer.mozilla.org');
     },
+    /**
+     * Interrupts the default click event on relative links inside
+     * the shadow dom and scrolls to the targeted anchor
+     * @param {Object} shadow - the shadow dom root
+     * @param {Array} relativeLinks - all relative links inside the shadow dom
+     */
+    scrollToAnchors: function(shadow, relativeLinks) {
+        relativeLinks.forEach(function(relativeLink) {
+            relativeLink.addEventListener('click', function(event) {
+                event.preventDefault();
+                shadow.querySelector(relativeLink.hash).scrollIntoView();
+            });
+        });
+    },
     /**
      * Hides the default example and shows the custom block
      * @param {object} customBlock - The HTML section to show

js/editor.js

@@ -80,6 +80,8 @@
 
         shadow.appendChild(document.importNode(content, true));
         setOutputHeight(shadow.querySelector('div'));
+        mceUtils.openLinksInNewTab(shadow.querySelectorAll('a[href^="http"]'));
+        mceUtils.scrollToAnchors(shadow, shadow.querySelectorAll('a[href^="#"]'));
     }
 
     /**