fix(sidenav): don't log an error when waiting for an instance.

* The `$mdSidenav` service was logging errors, even if the option to wait for an asynchronous instance was passed. This changes it to only log if the lookup for the instance is synchronous.
* Fixes the error for an invalid sidenav instance name not being logged if the `enableWait` argument is passed.
* Adds info about the async argument of `$mdSidenav` in the docs.

Fixes #8308.

Closes #8326

Author: crisbeto

src/components/sidenav/sidenav.js

@@ -23,11 +23,17 @@ angular
  *
  * @description
  * `$mdSidenav` makes it easy to interact with multiple sidenavs
- * in an app.
+ * in an app. When looking up a sidenav instance, you can either look
+ * it up synchronously or wait for it to be initializied asynchronously.
+ * This is done by passing the second argument to `$mdSidenav`.
  *
  * @usage
  * <hljs lang="js">
  * // Async lookup for sidenav instance; will resolve when the instance is available
+ * $mdSidenav(componentId, true).then(function(instance) {
+ *   $log.debug( componentId + "is now ready" );
+ * });
+ * // Sync lookup for sidenav instance; this will resolve immediately.
  * $mdSidenav(componentId).then(function(instance) {
  *   $log.debug( componentId + "is now ready" );
  * });
@@ -75,8 +81,9 @@ function SidenavService($mdComponentRegistry, $mdUtil, $q, $log) {
   return function(handle, enableWait) {
     if ( angular.isUndefined(handle) ) return service;
 
-    var instance = service.find(handle);
-    return  !instance && (enableWait === true) ? service.waitFor(handle) :
+    var shouldWait = enableWait === true;
+    var instance = service.find(handle, shouldWait);
+    return  !instance && shouldWait ? service.waitFor(handle) :
             !instance && angular.isUndefined(enableWait) ? addLegacyAPI(service, handle) : instance;
   };
 
@@ -106,9 +113,11 @@ function SidenavService($mdComponentRegistry, $mdUtil, $q, $log) {
      * Synchronously lookup the controller instance for the specified sidNav instance which has been
      * registered with the markup `md-component-id`
      */
-    function findInstance(handle) {
+    function findInstance(handle, shouldWait) {
       var instance = $mdComponentRegistry.get(handle);
-      if(!instance) {
+
+      if (!instance && !shouldWait) {
+
         // Report missing instance
         $log.error( $mdUtil.supplant(errorMsg, [handle || ""]) );
 
@@ -124,7 +133,7 @@ function SidenavService($mdComponentRegistry, $mdUtil, $q, $log) {
      * Deferred lookup of component instance using $component registry
      */
     function waitForInstance(handle) {
-      return $mdComponentRegistry.when(handle);
+      return $mdComponentRegistry.when(handle).catch($log.error);
     }
 }
 /**
@@ -263,7 +272,7 @@ function SidenavDirective($mdMedia, $mdUtil, $mdConstant, $mdTheming, $animate,
     if (!angular.isDefined(attr.mdDisableBackdrop)) {
       backdrop = $mdUtil.createBackdrop(scope, "_md-sidenav-backdrop md-opaque ng-enter");
     }
-    
+
     element.addClass('_md');     // private md component indicator for styling
     $mdTheming(element);
 
@@ -277,7 +286,7 @@ function SidenavDirective($mdMedia, $mdUtil, $mdConstant, $mdTheming, $animate,
     });
 
     scope.$on('$destroy', function(){
-      backdrop && backdrop.remove()
+      backdrop && backdrop.remove();
     });
 
     scope.$watch(isLocked, updateIsLocked);