JS Prototypal Inheritance CheckingAccount.js

function BankAccount(ownerName, begBalance) {
    var accountNumber = new Date().getTime() + '';
    
    this.ownerName = ownerName;
    this.balance = begBalance;
    
    this.getAccountNumber = function() { return accountNumber; };
}

BankAccount.prototype.deposit = function(amount) {
    this.balance += amount;
    return this.balance;
};
BankAccount.prototype.withdraw = function(amount) {
    this.balance -= amount;
    return this.balance;
};

function CheckingAccount(ownerName, begBalance, overdraftEnabled) {
    BankAccount.call(this, ownerName, begBalance);
    this.overdraftEnabled = overdraftEnabled || false;
}

CheckingAccount.prototype = Object.create(BankAccount.prototype);
CheckingAccount.prototype.constructor = CheckingAccount;

CheckingAccount.prototype.orderChecks = function() { return 'Checks have been ordered for Account: ' + this.getAccountNumber(); };

CheckingAccount.prototype.withdraw = function(amount) {
    if ( this.overdraftEnabled || amount <= this.balance ) {
        this.balance -= amount;
        return this.balance;
    } else {
        return "NSF";
    }
};

var chkAcct = new CheckingAccount('Joe Smith', 100, true);