transfer.js

function Account(code, balance) {
  return {
    get code(){ return code; },
    get balance(){ return balance; },
    increase: function(by){ balance += by; },
    decrease: function(by){ balance -= by; }
  };
}

function Bank(){
  var accounts = {};
  return {
    openAccount: function(code, initialBalance){
      accounts[code] = Account(code, initialBalance);
    },
    accountByCode: function(code){ return accounts[code]; }
  }
}

Transfer = Context(
function(bank, from, to, amount) {
  Source = bank.accountByCode(from);
  Destination = bank.accountByCode(to);
  Amount = amount;

  Source.give();
}, {
  Amount: {},
  Source: {
    give: function() {
      if(Source.balance < Amount){
        throw new Error("Insufficient funds.");
      }
      Source.decrease(Amount);
      Destination.receive();
    }
  },
  Destination: {
    receive: function() {
      Destination.increase(Amount);
    }
  }
});


var bank = Bank();
bank.openAccount("alice", 132);
bank.openAccount("bob", 23);

console.log("Before:");
console.log("alice ", bank.accountByCode("alice").balance);
console.log("bob ", bank.accountByCode("bob").balance);

Transfer(bank, "alice", "bob", 100);

console.log("After:");
console.log("alice", bank.accountByCode("alice").balance);
console.log("bob", bank.accountByCode("bob").balance);




// DCI implementation
function Context(init, roles, debug){
	// scoped role players
	var sfn = "  var " + Object.keys(roles).join(",") + ";\n";
	// creates the function
	var mkName = function(role, fn){ return role + "$" + fn; };  
	// redirects all role method calls
	var fixMethod = function(fn){
		fn = fn.toString();
		for(var roleName in roles){
			var role = roles[roleName];
			for(var fnName in role){
				// replaces Role.method(arg1,arg2,arg3) with
				//     with Role$method.call(Role, arg1, arg2, arg3)
				var rx = new RegExp( "(?!\\.)" + roleName + "\\s*\\.\\s*" + fnName + "\\s*\\(", "g");
				fn = fn.replace(rx,  mkName(roleName, fnName) + ".call(" + roleName + ",");
			}
		}
		// hack-fix Role$method.call(Arg,)
		fn = fn.replace(/,\)/g, ")");
		return fn;
	};
	// define role methods in to the context
	var methods = [];
	for(var roleName in roles){
		var role = roles[roleName];
		for(var fnName in role){
			methods.push("  var " + mkName(roleName, fnName) + " = "  + fixMethod(role[fnName]));
		}
	}
	sfn += methods.join(";\n") + ";\n";
	// return the init
	sfn += "  return (" + fixMethod(init) + ").apply(null, arguments);";

	if(debug){ 
		console.log(sfn);
	}
	return (new Function(sfn));
}

Transfer = (function(){
  var Amount,Source,Destination;
  var Source$give = function () {
      if(Source.balance < Amount){
        throw new Error("Insufficient funds.");
      }
      Source.decrease(Amount);
      Destination$receive.call(Destination);
    };
  var Destination$receive = function () {
      Destination.increase(Amount);
    };
  return (function (bank, from, to, amount) {
  Source = bank.accountByCode(from);
  Destination = bank.accountByCode(to);
  Amount = amount;

  Source$give.call(Source);
}).apply(null, arguments);
});