Fix version menu bug

spec/_static/javascripts/version_dropdown.js

@@ -1,46 +1,140 @@
-function assign_href(a, url, path) {
-    fetch(url + "/" + path).then(response => {
+/**
+* Returns a promise for resolving a URL corresponding to a versioned resource (if one exists).
+*
+* @private
+* @param {string} url - base URL
+* @param {string} path - resource path
+* @returns {Promise} promise which resolves a resource URL
+*/
+function href(url, path) {
+    const defaultURL = url + "/index.html";
+    url += "/" + path;
+
+    // If a versioned resource exists, return the resource's URL; otherwise, return a default URL:
+    const opts = {
+        'method': 'HEAD'
+    };
+    return fetch(url, opts).then(onResponse).catch(onError);
+
+    /**
+    * Callback invoked upon successfully resolving a resource.
+    *
+    * @private
+    * @param {Object} response - response object
+    */
+    function onResponse(response) {
         if (response.ok) {
-            a.href = url + "/" + path;
-        } else {
-            a.href = url + "/index.html";
+            return url;
         }
-    }).catch(error => {
-        a.href = url + "/index.html";
-    });
+        return defaultURL;
+    }
+
+    /**
+    * Callback invoked upon failing to resolve a resource.
+    *
+    * @private
+    * @param {Error} error - error object
+    */
+    function onError(error) {
+        return defaultURL;
+    }
 }
 
-function add_version_dropdown(json_loc, target_loc, text) {
-    var dropdown = document.createElement("div");
+/**
+* Adds a version dropdown menu with custom URL paths depending on the current page.
+*
+* @param {string} json_loc - JSON URL
+* @param {string} target_loc - target URL
+* @param {string} text - text
+* @returns {Promise} promise which resolves upon adding a version menu
+*/
+async function add_version_dropdown(json_loc, target_loc, text) {
+    const dropdown = document.createElement("div");
     dropdown.className = "md-flex__cell md-flex__cell--shrink dropdown";
-    var button = document.createElement("button");
+
+    const button = document.createElement("button");
     button.className = "dropdownbutton";
-    var content = document.createElement("div");
+
+    const 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|array_api/)[1];
+
+    const opts = {
+        'method': 'GET'
+    };
+    await fetch(json_loc, opts).then(onResponse).then(onVersions).catch(onError);
+
+    /**
+    * Callback invoked upon resolving a resource.
+    *
+    * @private
+    * @param {Object} response - response object
+    */
+    function onResponse(response) {
+        return response.json();
+    }
+
+    /**
+    * Callback invoked upon resolving a JSON resource.
+    *
+    * @private
+    * @param {Object} versions - versions object
+    * @returns {Promise} promise which resolves upon processing version data
+    */
+    async function onVersions(versions) {
+        // Resolve the current browser URL:
+        const currentURL = window.location.href;
+
+        // Check whether the user is currently on a resource page (e.g., is viewing the specification for a particular function):
+        let path = currentURL.split(/_site|array\-api/)[1];
+
+        // Extract the resource subpath:
         if (path) {
             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);
-                }
+        } else {
+            path = "";
+        }
+        // For each version, create an anchor element and attempt to resolve a given resource for that version...
+        const promises = [];
+        const el = [];
+        for (let key in versions) {
+            if (versions.hasOwnProperty(key)) {
+                let a = document.createElement("a");
+                a.innerHTML = key;
+                a.title = key;
+                el.push(a);
+                promises.push(href(target_loc + versions[key], path));
             }
         }
-    }).done(function() {
+        // Resolve all resource URLs:
+        const urls = await Promise.all(promises);
+
+        // Append the version links to the dropdown menu:
+        for (let i = 0; i < urls.length; i++) {
+            let a = el[i];
+            a.href = urls[i];
+            content.appendChild(a);
+        }
+        // Set the button text:
         button.innerHTML = text;
-    }).fail(function() {
+
+        // Append dropdown:
+        $(".navheader").append(dropdown);
+    }
+
+    /**
+    * Callback invoked upon failing to resolve a resource.
+    *
+    * @private
+    */
+    function onError() {
         button.innerHTML = "Other Versions Not Found";
-    }).always(function() {
+
+        // Append dropdown:
         $(".navheader").append(dropdown);
-    });
+    }
 };