Added keycodes dict for readability

lms/static/js/my_courses_dropdown.js

 $(document).ready(function() {
     'use strict';
 
-  // define variables for code legibility
+    // define variables for code legibility
     var dropdownMenuToggle = $('.dropdown');
     var dropdownMenu = $('.dropdown-menu');
     var menuItems = dropdownMenu.find('a');
 
-  // bind menu toggle click for later use
+    var keyCodes = {
+        leftArrow: 37,
+        upArrow: 38,
+        rightArrow: 39,
+        downArrow: 40,
+        tab: 9,
+        escape: 27,
+        space: 32
+    };
+
+
+    // bind menu toggle click for later use
     dropdownMenuToggle.toggle(function() {
         dropdownMenu.addClass('expanded').find('a').first().focus();
         dropdownMenuToggle.addClass('active').attr('aria-expanded', 'true');
@@ -15,47 +26,49 @@ $(document).ready(function() {
         dropdownMenuToggle.removeClass('active').attr('aria-expanded', 'false').focus();
     });
 
-  // catch keypresses when focused on dropdownMenuToggle (we only care about spacebar keypresses here)
+    // catch keypresses when focused on dropdownMenuToggle (we only care about spacebar keypresses here)
     dropdownMenuToggle.on('keydown', function(event) {
-    // if space key pressed
-        if (event.which == 32) {
+        // if space key pressed
+        if (event.which === keyCodes.space) {
             dropdownMenuToggle.click();
             event.preventDefault();
         }
     });
 
-  // catch keypresses when inside dropdownMenu (we want to catch spacebar; escape; up arrow or shift+tab; and down arrow or tab)
+    // catch keypresses when inside dropdownMenu
+    // (we want to catch spacebar; escape; up arrow or shift+tab; and down arrow or tab)
     dropdownMenu.on('keydown', function(event) {
         catchKeyPress($(this), event);
     });
 
     function catchKeyPress(object, event) {
-    // get currently focused item
+        // get currently focused item
         var focusedItem = jQuery(':focus');
 
-    // get the number of focusable items
+        // get the number of focusable items
         var numberOfMenuItems = menuItems.length;
 
-    // get the index of the currently focused item
+        // get the index of the currently focused item
         var focusedItemIndex = menuItems.index(focusedItem);
 
-    // var to store next focused item index
+        // var to store next focused item index
         var itemToFocusIndex;
 
-    // if space key pressed
-        if (event.which == 32) {
+        // if space key pressed
+        if (event.which === keyCodes.space) {
             dropdownMenuToggle.click();
             event.preventDefault();
         }
 
-    // if escape key pressed
-        if (event.which == 27) {
+        // if escape key pressed
+        if (event.which === keyCodes.escape) {
             dropdownMenuToggle.click();
             event.preventDefault();
         }
 
         // if up arrow key pressed or shift+tab else down key or tab is pressed
-        if (event.which === 38 || (event.which === 9 && event.shiftKey)) {
+        if (event.which === keyCodes.upArrow || event.which === keyCodes.leftArrow ||
+            (event.which === keyCodes.tab && event.shiftKey)) {
             // if first item go to last
             if (focusedItemIndex === 0) {
                 menuItems.last().focus();
@@ -64,7 +77,8 @@ $(document).ready(function() {
                 menuItems.get(itemToFocusIndex).focus();
             }
             event.preventDefault();
-        } else if (event.which === 40 || event.which === 9) {
+        } else if (event.which === keyCodes.downArrow || event.which === keyCodes.rightArrow ||
+            event.which === keyCodes.tab) {
             // if last item go to first
             if (focusedItemIndex === numberOfMenuItems - 1) {
                 menuItems.first().focus();