Refresh page when switching specification versions

PR-URL: #628
Reviewed-by: Athan Reines <[email protected]>
Reviewed-by: Ralf Gommers <[email protected]>

Author: kgryte

spec/_static/javascripts/version_dropdown.js

@@ -0,0 +1,44 @@
+function assign_href(a, url, path) {
+    fetch(url + "/" + path).then(response => {
+        if (response.ok) {
+            a.href = url + "/" + path;
+        } else {
+            a.href = url + "/index.html";
+        }
+    }).catch(error => {
+        a.href = url + "/index.html";
+    });
+}
+
+function add_version_dropdown(json_loc, target_loc, text) {
+    var dropdown = document.createElement("div");
+    dropdown.className = "md-flex__cell md-flex__cell--shrink dropdown";
+    var button = document.createElement("button");
+    button.className = "dropdownbutton";
+    var content = document.createElement("div");
+    content.className = "dropdown-content md-hero";
+    dropdown.appendChild(button);
+    dropdown.appendChild(content);
+    $.getJSON(json_loc, function(versions) {
+        var currentURL = window.location.href;
+        var path = currentURL.split("_site")[1];
+        path = path.split("/");
+        path = path.slice(2, path.length);
+        path = path.join("/");
+        for (var key in versions) {
+            if (versions.hasOwnProperty(key)) {
+                var a = document.createElement("a");
+                a.innerHTML = key;
+                a.title = key;
+                assign_href(a, target_loc + versions[key], path);
+                content.appendChild(a);
+            }
+        }
+    }).done(function() {
+        button.innerHTML = text;
+    }).fail(function() {
+        button.innerHTML = "Other Versions Not Found";
+    }).always(function() {
+        $(".navheader").append(dropdown);
+    });
+};