2 files changed, 46 insertions, 14 deletions

diff --git a/background/storage.js b/background/storage.js
index 682f933..c2160b0 100644
--- a/background/storage.js
+++ b/background/storage.js
@@ -16,6 +16,7 @@
  * IMPORT make_once
  * IMPORT browser
  * IMPORT is_chrome
+ * IMPORT observables
  * IMPORTS_END
  */
 
@@ -98,7 +99,8 @@ async function list(prefix)
     for (let item of await get_list_var(name))
 	map.set(item, await get(prefix + item));
 
-    return {map, prefix, name, listeners : new Set(), lock : make_lock()};
+    return {map, prefix, name, observable: observables.make(),
+	    lock: make_lock()};
 }
 
 var list_by_prefix = {};
@@ -121,7 +123,7 @@ exports.add_change_listener = function (cb, prefixes=list_prefixes)
 	prefixes = [prefixes];
 
     for (let prefix of prefixes)
-	list_by_prefix[prefix].listeners.add(cb);
+	observables.subscribe(list_by_prefix[prefix].observable, cb);
 }
 
 exports.remove_change_listener = function (cb, prefixes=list_prefixes)
@@ -130,13 +132,7 @@ exports.remove_change_listener = function (cb, prefixes=list_prefixes)
 	prefixes = [prefixes];
 
     for (let prefix of prefixes)
-	list_by_prefix[prefix].listeners.delete(cb);
-}
-
-function broadcast_change(change, list)
-{
-    for (let listener_callback of list.listeners)
-	listener_callback(change);
+	observables.unsubscribe(list_by_prefix[prefix].observable, cb);
 }
 
 /* Prepare some hepler functions to get elements of a list */
@@ -198,7 +194,7 @@ async function _set_item(item, value, list)
 	new_val : value
     };
 
-    broadcast_change(change, list);
+    observables.broadcast(list.observable, change);
 
     return old_val;
 }
@@ -236,7 +232,7 @@ async function _remove_item(item, list)
 	new_val : undefined
     };
 
-    broadcast_change(change, list);
+    observables.broadcast(list.observable, change);
 
     return old_val;
 }
@@ -282,7 +278,7 @@ async function _replace_item(old_item, new_item, list, new_val=undefined)
 	new_val : undefined
     };
 
-    broadcast_change(change, list);
+    observables.broadcast(list.observable, change);
 
     list.map.set(new_item, new_val);
 
@@ -290,7 +286,7 @@ async function _replace_item(old_item, new_item, list, new_val=undefined)
     change.old_val = undefined;
     change.new_val = new_val;
 
-    broadcast_change(change, list);
+    observables.broadcast(list.observable, change);
 
     return old_val;
 }
@@ -375,7 +371,7 @@ exports.clear = async function ()
 	for (let [item, val] of list_entries_it(list)) {
 	    change.item = item;
 	    change.old_val = val;
-	    broadcast_change(change, list);
+	    observables.broadcast(list.observable, change);
 	}
 
 	list.map = new Map();
diff --git a/common/observable.js b/common/observable.js
new file mode 100644
index 0000000..1fb0b0a
--- /dev/null
+++ b/common/observable.js
@@ -0,0 +1,36 @@
+/**
+ * part of Hachette
+ * Facilitate listening to events
+ *
+ * Copyright (C) 2021 Wojtek Kosior
+ * Redistribution terms are gathered in the `copyright' file.
+ */
+
+function make()
+{
+    return new Set();
+}
+
+function subscribe(observable, cb)
+{
+    observable.add(cb);
+}
+
+function unsubscribe(observable, cb)
+{
+    observable.delete(cb);
+}
+
+function broadcast(observable, event)
+{
+    for (const callback of observable)
+	callback(event);
+}
+
+const observables = {make, subscribe, unsubscribe, broadcast};
+
+/*
+ * EXPORTS_START
+ * EXPORT observables
+ * EXPORTS_END
+ */