extract observables implementation from storage.js

1 files changed, 36 insertions, 0 deletions

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
+ */