Add Proxy (ES5 + ES6 + CoffeeScript)

Author: Badacadabra

doc/GoF/Structural/Proxy/Proxy.dia

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+# Synopsis
+
+I need some cash, so I have to find an ATM (Automated Teller Machine).
+
+# Problem
+
+Money withdrawal is under control. Everyone has a personal bank account which is only accessible with a specific credit card and a related code.
+
+For this reason, we cannot interact directly with the "real" object (our bank account). We must interact with another object that will be responsible for the communication with the real object.
+
+# Solution
+
+We could consider an ATM as a proxy whose aim is to verify access to a bank account. Here the Proxy design pattern requires:
+
+  * An abstract representation of a financial entity (abstract class or interface)
+  * A concrete bank account which allows some operations
+  * A proxy (ATM) which secures these operations and delegates when necessary

doc/GoF/Structural/Proxy/Proxy.png

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+"use strict"
+
+# ==============================
+# ABSTRACT FINANCIAL ENTITY
+# ==============================
+
+class FinancialEntity
+    constructor: ->
+        throw new Error "You cannot instantiate an abstract class!" if @constructor is FinancialEntity
+
+    withdrawMoney: ->
+        throw new Error "You cannot call an abstract method!"
+
+# ==============================
+# CONCRETE BANK ACCOUNT
+# ==============================
+
+class BankAccount extends FinancialEntity
+    withdrawMoney: ->
+        "Enjoy the cash!"
+
+# ==============================
+# CONCRETE ATM 
+# ==============================
+
+class ATM extends FinancialEntity
+    constructor: (@_bankAccount) ->
+
+    withdrawMoney: (code) ->
+        throw type: "AuthenticationException", message: "Invalid code" if code isnt 1337
+        @_bankAccount.withdrawMoney()
+
+# ==============================
+# CLIENT CODE
+# ==============================
+
+bankAccount = new BankAccount
+proxy = new ATM bankAccount
+
+try
+    console.log proxy.withdrawMoney 1234 # Wrong code
+catch e
+    console.log "#{e.type} - #{e.message}" # AuthenticationException - Invalid code
+finally
+    console.log proxy.withdrawMoney 1337 # Enjoy the cash!

doc/GoF/Structural/Proxy/README.md

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+'use strict';
+
+// ==============================
+// ABSTRACT FINANCIAL ENTITY
+// ==============================
+
+var FinancialEntity = (function () {
+    function FinancialEntity() {
+        if (this.constructor === FinancialEntity) {
+            throw new Error("You cannot instantiate an abstract class!");
+        }
+    }
+
+    FinancialEntity.prototype.withdrawMoney = function () {
+        throw new Error("You cannot call an abstract method!");
+    };
+
+    return FinancialEntity;
+})();
+
+// ==============================
+// CONCRETE BANK ACCOUNT
+// ==============================
+
+var BankAccount = (function () {
+    function BankAccount() {}
+    BankAccount.prototype = Object.create(FinancialEntity.prototype);
+    BankAccount.prototype.constructor = BankAccount;
+
+    BankAccount.prototype.withdrawMoney = function () {
+        return "Enjoy the cash!";
+    };
+
+    return BankAccount;
+})();
+
+// ==============================
+// CONCRETE ATM 
+// ==============================
+
+var ATM = (function () {
+    var bankAccount;
+
+    function ATM(account) {
+        bankAccount = account;
+    }
+    ATM.prototype = Object.create(FinancialEntity.prototype);
+    ATM.prototype.constructor = ATM;
+
+    ATM.prototype.withdrawMoney = function (code) {
+        if (code !== 1337) {
+            throw {
+                type: "AuthenticationException",
+                message: "Invalid code"
+            };
+        }
+        return bankAccount.withdrawMoney();
+    };
+
+    return ATM;
+})();
+
+// ==============================
+// CLIENT CODE 
+// ==============================
+
+var bankAccount = new BankAccount(),
+    proxy = new ATM(bankAccount);
+
+try {
+    console.log(proxy.withdrawMoney(1234)); // Wrong code
+} catch (e) {
+    console.log(e.type + " - " + e.message); // AuthenticationException - Invalid code
+} finally {
+    console.log(proxy.withdrawMoney(1337)); // Enjoy the cash! 
+}

src/CoffeeScript/GoF/Structural/Proxy/Proxy.coffee

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+// ==============================
+// ABSTRACT FINANCIAL ENTITY
+// ==============================
+
+class FinancialEntity {
+    constructor() {
+        if (new.target !== undefined) {
+            throw new Error("You cannot instantiate an abstract class!");
+        }
+    } 
+
+    withdrawMoney() {
+        throw new Error("You cannot call an abstract method!");
+    }
+}
+
+// ==============================
+// CONCRETE BANK ACCOUNT
+// ==============================
+
+class BankAccount extends FinancialEntity {
+    withdrawMoney() {
+        return "Enjoy the cash!";
+    }
+}
+
+// ==============================
+// CONCRETE ATM 
+// ==============================
+
+class ATM extends FinancialEntity {
+    constructor(bankAccount) {
+        super();
+        this._bankAccount = bankAccount;
+    }
+
+    withdrawMoney(code) {
+        if (code !== 1337) {
+            throw {
+                type: "AuthenticationException",
+                message: "Invalid code"
+            };
+        }
+        return this._bankAccount.withdrawMoney();
+    }
+}
+
+// ==============================
+// CLIENT CODE
+// ==============================
+
+let bankAccount = new BankAccount(),
+    proxy = new ATM(bankAccount);
+
+try {
+    console.log(proxy.withdrawMoney(1234)); // Wrong code
+} catch (e) {
+    console.log(`${e.type} - ${e.message}`); // AuthenticationException - Invalid code
+} finally {
+    console.log(proxy.withdrawMoney(1337)); // Enjoy the cash! 
+}