refactor(menu): improve menu get lookup

If a `menuId` is not provided then it'll return the first menu found.
If a `menuId` is `left` or `right`, then it'll return the enabled menu
on that side. Otherwise, if a `menuId` is provided, then it'll try to
find the menu using the menu's `id` property. If a menu is not found
then it'll return `null`. If a menu id was provided, but was not found,
it will not fallback to finding any menu. Closes #5535

ionic/components/menu/menu-controller.ts

@@ -207,8 +207,9 @@ export class MenuController {
 
   /**
    * Used to enable or disable a menu. For example, there could be multiple
-   * left menus, but only one of them should be able to be dragged open.
-   * @param {boolean} shouldEnable  True if it should be enabled, false if not.
+   * left menus, but only one of them should be able to be opened at the same
+   * time. If there are multiple menus on the same side, then enabling one menu
+   * will also automatically disable all the others that are on the same side.
    * @param {string} [menuId]  Optionally get the menu by its id, or side.
    * @return {Menu}  Returns the instance of the menu, which is useful for chaining.
    */
@@ -249,24 +250,37 @@ export class MenuController {
   }
 
   /**
-   * Used to get a menu instance. If a `menuId` is not provided then it'll return
-   * the first menu found. If a `menuId` is provided, then it'll first try to find
-   * the menu using the menu's `id` attribute. If a menu is not found using the `id`
-   * attribute, then it'll try to find the menu by its `side` name.
+   * Used to get a menu instance. If a `menuId` is not provided then it'll
+   * return the first menu found. If a `menuId` is `left` or `right`, then
+   * it'll return the enabled menu on that side. Otherwise, if a `menuId` is
+   * provided, then it'll try to find the menu using the menu's `id`
+   * property. If a menu is not found then it'll return `null`.
    * @param {string} [menuId]  Optionally get the menu by its id, or side.
    * @return {Menu}  Returns the instance of the menu if found, otherwise `null`.
    */
   get(menuId?: string): Menu {
-    if (menuId) {
-      // first try by "id"
-      let menu = this._menus.find(m => m.id === menuId);
-      if (menu) return menu;
+    var menu: Menu;
 
-      // not found by "id", next try by "side"
+    if (menuId === 'left' || menuId === 'right') {
+      // there could be more than one menu on the same side
+      // so first try to get the enabled one
       menu = this._menus.find(m => m.side === menuId && m.enabled);
       if (menu) return menu;
+
+      // didn't find a menu side that is enabled
+      // so try to get the first menu side found
+      return this._menus.find(m => m.side === menuId) || null;
+
+    } else if (menuId) {
+      // the menuId was not left or right
+      // so try to get the menu by its "id"
+      return this._menus.find(m => m.id === menuId) || null;
     }
 
+    // return the first enabled menu
+    menu = this._menus.find(m => m.enabled);
+    if (menu) return menu;
+
     // get the first menu in the array, if one exists
     return (this._menus.length ? this._menus[0] : null);
   }

ionic/components/menu/menu.ts

@@ -370,15 +370,29 @@ export class Menu extends Ion {
 
   /**
    * Used to enable or disable a menu. For example, there could be multiple
-   * left menus, but only one of them should be able to be dragged open.
+   * left menus, but only one of them should be able to be opened at the same
+   * time. If there are multiple menus on the same side, then enabling one menu
+   * will also automatically disable all the others that are on the same side.
    * @param {boolean} shouldEnable  True if it should be enabled, false if not.
    * @return {Menu}  Returns the instance of the menu, which is useful for chaining.
    */
   enable(shouldEnable: boolean): Menu {
     this.enabled = shouldEnable;
     if (!shouldEnable && this.isOpen) {
+      // close if this menu is open, and should not be enabled
       this.close();
     }
+
+    if (shouldEnable) {
+      // if this menu should be enabled
+      // then find all the other menus on this same side
+      // and automatically disable other same side menus
+      let sameSideMenus = this._menuCtrl
+                            .getMenus()
+                            .filter(m => m.side === this.side && m !== this)
+                            .map(m => m.enabled = false);
+    }
+
     return this;
   }