Question

I want to use objectoriented Javascript, but the behaviour of my “object” is not as I expect them to be.

This is my object:

var Test = function(a){
    var variable = a;

    this.getA = function(){
        return this.variable;
    }

    this.setA = function(a){
        this.variable = a;
    }
}

Now I run this code:

var a = new Test("foo");
var b = new Test("bar");

alert(a.getA());                //undefined, but "foo" expected
alert(a.getA() == b.getA());    //true, but false expected

alert(a.variable);              //undefined, as expected

a.variable = "whatever";
alert(a.getA());                //"whatever", but undefined expected
alert(a.variable);              //"whatever", but undefined expected

a.setA("somewhere");
alert(a.getA());                //"somewhere", as expected
alert(a.variable);              //"somewhere", but undefined expected

Does anyone know how to create a functioning object, without the need to call “setA(a)” at the beginning, and with object encapsulation not allowing a.variable = “whatever”;?

Answer 1

If you’re encapsulating the value of a, you don’t need to use this.variable to access the value, simply changing this.variable to variable should fix the issue.

Variables have functional scope, so var variable defines a variable that is in scope not only for Test, but also for setA and getA:

var Test = function(a){
    var variable = a;

    this.getA = function(){
        //you want to access the variable,
        //not the property on the instance
        return variable;

    }

    this.setA = function(a){
        variable = a;
    }
}