Calculate transaction delta

tshemsedinov · tshemsedinov · commit 6de4f73b68a5 · 2018-02-21T04:47:28.000+02:00
diff --git a/JavaScript/4-delta.js b/JavaScript/4-delta.js
@@ -0,0 +1,73 @@
+'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 = {};
+    },
+    clone: () => {
+      console.log('clone transaction');
+      const cloned = Transaction.start(data);
+      Object.assign(cloned.delta, delta);
+      return cloned;
+    },
+    delta: () => delta
+  };
+
+  const proxy = new Proxy(data, {
+    get(target, key) {
+      if (key === Symbol.iterator) {
+        const changes = Object.keys(delta);
+        const keys = Object.keys(target).concat(changes);
+        const props = keys.filter((x, i, a) => a.indexOf(x) === i);
+        return props[Symbol.iterator]();
+      }
+      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;
+    }
+  });
+  return proxy;
+};
+
+// Usage
+
+const data = { name: 'Marcus Aurelius', city: 'Rome', born: 121 };
+
+const transaction = Transaction.start(data);
+console.dir({ data, transaction, delta: transaction.delta() });
+
+transaction.name = 'Mao Zedong';
+transaction.born = 1893;
+console.dir({ data, transaction, delta: transaction.delta() });
+
+transaction.commit();
+console.dir({ data, transaction, delta: transaction.delta() });
+
+transaction.city = 'Shaoshan';
+console.dir({ data, transaction, delta: transaction.delta() });
+
+transaction.rollback();
+console.dir({ data, transaction, delta: transaction.delta() });
