关于对象和函数的用法的困惑

Question

especially the 'this' keyword. Like below code, using function, I can avoid duplication of code already. The more I read sample code the more confuse I'm, it's like things can be achieved this way, but there are other (complex) ways to do it.. or I'm wrong?

var bob = {
    firstName: "Bob",
    lastName: "Jones",
    phoneNumber: "(650) 777-7777",
    email: "bob.jones@example.com"
};

var mary = {
    firstName: "Mary",
    lastName: "Johnson",
    phoneNumber: "(650) 888-8888",
    email: "mary.johnson@example.com"
};

// printPerson added here
function printPerson(person){
    console.log(person.firstName + " " + person.lastName);

}

printPerson(bob);
printPerson(mary);

my question is, how to improve above code by using this keyword. For now, I already seeing OOP (or I'm wrong?).

extra : Need no constructor or something more complex like new keyword.

Answer 1

function Person(firstName, lastName, phoneNumber, eMail) {
    var that = this;
    that.firstName = firstName;
    that.lastName = lastName;
    that.phoneNumber = phoneNumber;
    that.eMail = eMail;
    return {
        printPerson: function() {
            console.log(that.firstName + " " + that.lastName);
        }
    }
};

var person1 = Person("Bruce", "Wayne", "1234", "bane@joker.com");
person1.printPerson();

var person2 = Person("Kent", "Clark", "4321", "me@thesky.com");
person2.printPerson();

Answer 2

The problem of the printPerson approach is when you need "polymorphism"; ie you want to print an object but you don't want to know what kind of object it is: suppose

function newPerson(firstName, lastName) {
    return { firstName: firstName,
             lastName: lastName };
}

function newPet(name, kind) {
    return { name: name,
             kind: kind };
}

function printPerson(person) {
    console.log(person.firstName + " " + person.lastName);
}

function printPet(pet) {
    console.log(pet.name + " (a nice " + pet.kind + ")");
}

var p1 = newPerson("Andrea", "Griffini");
var p2 = newPet("Tobi", "cat");

printPerson(p1);
printPet(p2);

the problem however is... suppose you're given an object x and you need to print it, but you don't know if it's a person or a pet... how do you do? Solution 1 is checking with if / then

if (x.firstName) {
    printPerson(x);
} else {
    printPet(x);
}

but this is annoying because if you add later another type of object you need to fix that.

The OOP solution is to change the code slightly

function Person(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.print = function() {
        console.log(this.firstName + " " + this.lastName);
    };
}

function Pet(name, kind) {
    this.name = name;
    this.kind = kind;
    this.print = function() {
        console.log(this.name + " (a nice " + this.kind + ")");
    };
}

and now the use becomes

var p1 = new Person("Andrea", "Griffini");
var p2 = new Pet("Tobi", "cat");

p1.print();
p2.print();

and the problem for a general x is just x.print() .

Basically the idea is to keep the data (eg firstName , lastName ) and the code (eg the implementation of print ) together for each type of object. You can add a new object type by just implementing the constructor and without the need to change other code that will "magically" end up calling the correct version of print .