Implement getOwnPropertyDescriptor handler

tshemsedinov · tshemsedinov · commit ea367a849413 · 2018-02-21T04:47:05.000+02:00
diff --git a/JavaScript/3-descriptor.js b/JavaScript/3-descriptor.js
@@ -0,0 +1,64 @@
+'use strict';
+
+function Transaction() {}
+
+Transaction.start = (data) => {
+  console.log('start transaction');
+  let delta = {};
+
+  const methods = {
+    commit: () => {
+      console.log('commit transaction');
+      Object.assign(data, delta);
+      delta = {};
+    },
+    rollback: () => {
+      console.log('rollback transaction');
+      delta = {};
+    }
+  };
+
+  return new Proxy(data, {
+    get(target, key) {
+      if (methods.hasOwnProperty(key)) return methods[key];
+      if (delta.hasOwnProperty(key)) return delta[key];
+      return target[key];
+    },
+    getOwnPropertyDescriptor: (target, key) => (
+      Object.getOwnPropertyDescriptor(
+        delta.hasOwnProperty(key) ? delta : target, key
+      )
+    ),
+    set(target, key, val) {
+      console.log('set', key, val);
+      if (target[key] === val) delete delta[key];
+      else delta[key] = val;
+      return true;
+    }
+  });
+};
+
+// Usage
+
+const data = { name: 'Marcus Aurelius', city: 'Rome', born: 121 };
+
+const transaction = Transaction.start(data);
+console.log(JSON.stringify(data), JSON.stringify(transaction));
+console.dir({ data, transaction });
+
+transaction.name = 'Mao Zedong';
+transaction.born = 1893;
+console.log('JSON:', JSON.stringify(data), JSON.stringify(transaction));
+console.dir({ data, transaction });
+
+transaction.commit();
+console.log('JSON:', JSON.stringify(data), JSON.stringify(transaction));
+console.dir({ data, transaction });
+
+transaction.city = 'Shaoshan';
+console.log('JSON:', JSON.stringify(data), JSON.stringify(transaction));
+console.dir({ data, transaction });
+
+transaction.rollback();
+console.log('JSON:', JSON.stringify(data), JSON.stringify(transaction));
+console.dir({ data, transaction });
