Javascript constructor behaviour

Question

I have a question in respect of the js constructor function. I have the following code:

    var PersonConstructorFunction = function (firstName, lastname, gender) {
    this.personFirstName = firstName;
    this.personLastName = lastname;
    this.personGender = gender;

    this.personFullName = function () {
        return this.personFirstName + " " + this.personLastName;
    };

    this.personGreeting = function (person) {

            if (this.personGender == "male") {
                return "Hello Mr." + this.personFullName();
            }

            else if (this.personGender == "female") {
                return "Hello Mrs." + this.personFullName();
            }
         else {
            return "Hello There!";
        }
    };
};

var p =  new PersonConstructorFunction("Donald", "Duck", "male");
p2 = new PersonConstructorFunction("Lola", "Bunney", "female");
document.write(p2.personGreeting(p2) + " ");

The result is quite obvious - --Hello Mrs. Lola Bunney--

The question is: There are two equivalent objects p and p2 with the same number of properties and methods. I can't understand the following behaviour when I call the personGreeting method of one object and pass the second object as the argument:

**document.write(p2.personGreeting(p) + " ");**

in this case I get --Hello Mrs. Lola Bunney-- but what about the p object that is passed as the argument?

personGreeting gets the person object, determines their gender and bsed on the result shows appropriate greetings.

Resently I learned C# and constructors there works similarly I guess.

In personGreeting, the this keyword isn't referring to your p object (that's the person parameter since you passed p as an argument, which you never use in that function). — ajp15243
– ajp15243, Commented Apr 21, 2014 at 18:23
The way constructors (and, more generally, objects and inheritance) work in JavaScript is vastly different from how those things work in C#. — Pointy
– Pointy, Commented Apr 21, 2014 at 18:26
I think you need to rethink your personGreeting method. You're either going to wind up with it having a useless parameter (person) if you use this, or you're going to use person, in which case it makes no sense as a member method of the object. The only way it would make sense as a member method with a person parameter would be if it made use of both the object that contained it and the value that was passed to it. — JLRishe
– JLRishe, Commented Apr 21, 2014 at 18:35

Benjamin Trent · Accepted Answer · 2014-04-21 18:28:56Z

2

You are not doing anything with the passed parameter. Since you are utilizing this only the variables that are within your constructor are being called.

You COULD do person.personFullName(); and that would mean that the parameters member personFullName() would be called and not your constructors.

answered Apr 21, 2014 at 18:28

Benjamin Trent

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