Add simple transaction example

tshemsedinov · tshemsedinov · commit c4d2ad7ece42 · 2018-02-18T04:01:03.000+02:00
diff --git a/JavaScript/1-proxy.js b/JavaScript/1-proxy.js
@@ -0,0 +1,69 @@
+'use strict';
+
+function Transaction() {}
+
+Transaction.start = (data) => {
+  console.log('start transaction');
+  let delta = {};
+
+  const methods = {
+    commit: () => {
+      console.log('commit transaction');
+      Object.assign(data, delta);
+    },
+    rollback: () => {
+      console.log('rollback transaction');
+      delta = {};
+    }
+  };
+
+  return new Proxy(data, {
+    get(target, key) {
+      console.log('get', 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]();
+      }
+      return methods[key] || delta[key] || 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);
+
+transaction.name = 'Mao Zedong';
+transaction.born = 1893;
+
+console.log('data.name = ', data.name);
+console.log('transaction.name = ', transaction.name);
+
+transaction.commit();
+
+console.log('data.name = ', data.name);
+console.log('transaction.name = ', transaction.name);
+
+transaction.city = 'Shaoshan';
+
+console.log('data.city = ', data.city);
+console.log('transaction.city = ', transaction.city);
+
+transaction.rollback();
+
+console.log('data.city = ', data.city);
+console.log('transaction.city = ', transaction.city);
