Define calculated fields methods and example

Author: tshemsedinov

JavaScript/a-calculated.js

@@ -0,0 +1,23 @@
+'use strict';
+
+// Usage
+
+const data = { name: 'Marcus Aurelius', born: 121, city: 'Rome' };
+
+const cities = {
+  'Roman Empire': ['Rome']
+};
+
+const [obj, transaction] = Transaction.start(data, {
+  age() {
+    return (
+      new Date().getFullYear() -
+      new Date(this.born + '').getFullYear()
+    );
+  },
+  country() {
+    // implementation cann access cities index
+  }
+});
+
+console.dir({ age: obj.age, country: obj.country });