CODEWITHSUNDEEP
javascriptobject
guevarak12
guevarak12

Reputation: 75

Private function in Javascript constructor is not accessible publicly

I have this person object 

function person(first, last, age, eye) {
    this.firstName = first;
    this.lastName = last;
    this.age = age;
    this.eyeColor = eye;

    function sayName(){
        var full="";    
        full="Hello my name is "+this.firstName + " "+this.lastName;
    }
}

and have made an instance of this object 

var raul = new person("Raul","Zamora","19","brown")

I cannot figure out why the function sayName is not working. I am implementing it as such:

document.getElementById("sayName").innerHTML=raul.sayName();

where sayName is already defined as an id on the HTML part.

Upvotes: 0

Views: 71

Answers (3)

Dalorzo
Dalorzo

Reputation: 20014

Your function sayName does not "belong" to your Class, in order to do so you need to declare it using this or using propotype

Using this :

function person(first, last, age, eye) {
            this.sayName = function(){
                return "Hello my name is "+this.firstName + " "+this.lastName;
            }
        }

Using prototype :

person.prototype.sayName = function(){
     return "Hello my name is "+this.firstName + " "+this.lastName;
}

Additionally sayName was not returning anything.

Upvotes: 0

Bergi
Bergi

Reputation: 664599

You've got a local function declaration there. Make it a property of the object by assignment - just like you did write this.firstName = first not var firstName = first.

This will make it a method that is accessible from outside:

function person(first, last, age, eye) {
    this.firstName = first;
    this.lastName = last;
    this.age = age;
    this.eyeColor = eye;

    this.sayName = function sayName(){
        var full="Hello my name is "+this.firstName + " "+this.lastName;
    };
}

However, some objections:

  • Constructor names should be capitalized
  • Your sayName method needs to return the string, or your example invocation won't work
  • Using the prototype for values that can be shared amongst instances (such as methods) is preferable

So we get to

function Person(first, last, age, eye) {
    this.firstName = first;
    this.lastName = last;
    this.age = age;
    this.eyeColor = eye;
}
Person.prototype.sayName = function sayName(){
    return "Hello my name is "+this.firstName + " "+this.lastName;
};

var raul = new Person("Raul","Zamora","19","brown");
document.getElementById("sayName").textContent = raul.sayName();

Upvotes: 0

Denys Séguret
Denys Séguret

Reputation: 382170

It doesn't work because that sayName function is only visible in the scope of the constructor (and thus is totally useless).

To make that function available on instances, use 

person.prototype.sayName = function(){
   var full="Hello my name is "+this.firstName + " "+this.lastName;
   return full; // don't forget to return the string
}

For more details, I suggest this article from the MDN : Introduction to Object-Oriented JavaScript

Upvotes: 2

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