1 files changed, 11 insertions, 17 deletions
diff --git a/common/observable.js b/common/observable.js
index 1fb0b0a..02f1c1b 100644
--- a/common/observable.js
+++ b/common/observable.js
@@ -6,28 +6,22 @@
  * Redistribution terms are gathered in the `copyright' file.
  */
 
-function make()
-{
-    return new Set();
-}
+const make = (value=undefined) => ({value, listeners: new Set()});
+const subscribe = (observable, cb) => observable.listeners.add(cb);
+const unsubscribe = (observable, cb) => observable.listeners.delete(cb);
 
-function subscribe(observable, cb)
-{
-    observable.add(cb);
-}
-
-function unsubscribe(observable, cb)
-{
-    observable.delete(cb);
-}
+const silent_set = (observable, value) => observable.value = value;
+const broadcast = (observable, ...values) =>
+      observable.listeners.forEach(cb => cb(...values));
 
-function broadcast(observable, event)
+function set(observable, value)
 {
-    for (const callback of observable)
-	callback(event);
+    const old_value = observable.value;
+    silent_set(observable, value);
+    broadcast(observable, value, old_value);
 }
 
-const observables = {make, subscribe, unsubscribe, broadcast};
+const observables = {make, subscribe, unsubscribe, broadcast, silent_set, set};
 
 /*
  * EXPORTS_START