Add undo example

Author: tshemsedinov

JavaScript/2-undo.js

@@ -0,0 +1,84 @@
+'use strict';
+
+class AccountCommand {
+  constructor(account, amount) {
+    this.account = account;
+    this.amount = amount;
+  }
+  execute() {
+    throw new Error('Command.execute() is not implemented');
+  }
+  undo() {
+    throw new Error('Command.undo() is not implemented');
+  }
+}
+
+class Withdraw extends AccountCommand {
+  execute() {
+    this.account.balance -= this.amount;
+  }
+  undo() {
+    this.account.balance += this.amount;
+  }
+}
+
+class Income extends AccountCommand {
+  execute() {
+    this.account.balance += this.amount;
+  }
+  undo() {
+    this.account.balance -= this.amount;
+  }
+}
+
+class BankAccount {
+  constructor(name) {
+    this.name = name;
+    this.balance = 0;
+  }
+}
+
+class Bank {
+  constructor() {
+    this.commands = [];
+  }
+  operation(account, amount) {
+    const Command = amount < 0 ? Withdraw : Income;
+    const command = new Command(account, Math.abs(amount));
+    command.execute();
+    this.commands.push(command);
+  }
+  undo(count) {
+    for (let i = 0; i < count; i++) {
+      const command = this.commands.pop();
+      command.undo();
+    }
+  }
+  showOperations() {
+    const output = [];
+    for (const command of this.commands) {
+      output.push({
+        operation: command.constructor.name,
+        account: command.account.name,
+        amount: command.amount
+      });
+    }
+    console.table(output);
+  }
+}
+
+// Usage
+
+const bank = new Bank();
+const account1 = new BankAccount('Marcus Aurelius');
+bank.operation(account1, 1000);
+bank.operation(account1, -50);
+const account2 = new BankAccount('Antoninus Pius');
+bank.operation(account2, 500);
+bank.operation(account2, -100);
+bank.operation(account2, 150);
+bank.showOperations();
+console.table([account1, account2]);
+bank.undo(2);
+bank.showOperations();
+console.table([account1, account2]);