add getRegistrationById()

Author: wanderview

docs/index.bs

@@ -122,9 +122,8 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
 }
 </pre>
 
-<!-- TODO: expose getRegistrationById() -->
-<!-- TODO: uncontrol old clients that no longer match in Activate -->
 <!-- TODO: change scope logic -->
+<!-- TODO: uncontrol old clients that no longer match in Activate -->
 
 <section>
   <h2 id="motivations">Motivations</h2>
@@ -693,6 +692,7 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
         [NewObject] Promise&lt;ServiceWorkerRegistration&gt; register(USVString scriptURL, optional RegistrationOptions options = {});
 
         [NewObject] Promise&lt;any&gt; getRegistration(optional USVString clientURL = "");
+        [NewObject] Promise&lt;any&gt; getRegistrationById(DOMString id);
         [NewObject] Promise&lt;FrozenArray&lt;ServiceWorkerRegistration&gt;&gt; getRegistrations();
 
         void startMessages();
@@ -786,6 +786,20 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
         1. Return |promise|.
     </section>
 
+    <section algorithm="navigator-service-worker-getRegistrationById">
+      <h4 id="navigator-service-worker-getRegistrationById">{{ServiceWorkerContainer/getRegistrationById(id)}}</h4>
+
+      <dfn method for="ServiceWorkerContainer"><code>getRegistrationById(|id|)</code></dfn> method steps are:
+
+        1. Let |origin| be [=current settings object=]'s [=environment settings object/origin=].
+        1. Let |promise| be a new <a>promise</a>.
+        1. Run the following substeps <a>in parallel</a>
+            1. Let |registration| be the result of running the [=GetRegistration=] algorithm passing |origin| and |id| as the arguments.
+            1. If |registration| is null, resolve |promise| with undefined and abort these steps.
+            1. Resolve |promise| with the result of [=getting the service worker registration object=] that represents |registration| in |promise|'s [=relevant settings object=].
+        1. Return |promise|.
+    </section>
+
     <section algorithm="navigator-service-worker-getRegistrations">
       <h4 id="navigator-service-worker-getRegistrations">{{ServiceWorkerContainer/getRegistrations()}}</h4>