feat: open external links in new tab (#1222)

_includes/head.html

@@ -55,6 +55,7 @@
     <link rel="stylesheet" href="/public/css/index.css">
     <!-- JavaScript -->
     <script src="/public/js/switch-alt-link.js" async defer></script>
+    <script src="/public/js/external-links-new-tab.js" async defer></script>
     {% include ogp.html %}
     {% include google_analytics.html %}
 </head>

public/js/external-links-new-tab.js

@@ -0,0 +1,24 @@
+function onReady() {
+    return new Promise((resolve) => {
+        const readyState = document.readyState;
+        if (readyState === "interactive" || readyState === "complete") {
+            resolve();
+        } else {
+            window.addEventListener("DOMContentLoaded", resolve);
+        }
+    });
+}
+
+// If it is an external link, set target="_blank"
+function setExternalLinksOpenInNewTabs() {
+    var externalLinkNodeList = document.querySelectorAll("a[href^='http']:not([href*='jser.info'])")
+    var links = Array.prototype.slice.call(externalLinkNodeList);
+    // add _blank and track
+    links.forEach(function (link) {
+        if (!link.target) {
+            link.target = "_blank";
+        }
+    });
+}
+
+onReady().then(() => setExternalLinksOpenInNewTabs());