First commit.

react/src/ObservableProperty.tsx

@@ -0,0 +1,50 @@
+
+
+export type OnChangedHandler<VALUE_TYPE> = (newValue: VALUE_TYPE) => void;
+
+
+export class ObservableProperty<VALUE_TYPE> {
+
+    _value_type: VALUE_TYPE;
+    _on_changed_handlers: OnChangedHandler<VALUE_TYPE>[] = [];
+
+    constructor(default_value: VALUE_TYPE)
+    {
+        this._value_type = default_value;
+    }
+
+    addOnChangedHandler(handler: OnChangedHandler<VALUE_TYPE> ) : void
+    {
+        this._on_changed_handlers.push(handler);
+        handler(this._value_type);
+    }
+    removeOnChangedHandler(handler: OnChangedHandler<VALUE_TYPE> ) : void
+    {
+        let oldArray = this._on_changed_handlers;
+
+        let newArray: OnChangedHandler<VALUE_TYPE>[] = [];
+
+        let outIx = 0;
+        for (let i = 0; i < oldArray.length; ++i)
+        {
+            if (oldArray[i] !== handler)
+            {
+                newArray[outIx++]  = oldArray[i];
+            }
+        }
+        this._on_changed_handlers = newArray;
+    }
+
+    get() : VALUE_TYPE {
+        return this._value_type;
+    }
+
+    set(value: VALUE_TYPE) : void
+    {
+        this._value_type = value;
+
+        let t = this._on_changed_handlers; // take an copy in case removes happen while iteratiing.
+        t.forEach(c => c(value));
+    }
+
+};