Declaring a member function in JS

Question

I've tried two ways to declare a member function in JS:

function init() {
    var name = "Mozilla";
    function displayName() {
        alert(name);
    }
}
a = new init();
a.displayName()

And

function init() {
    var name = "Mozilla";
    displayName = function() {
        alert(name);
    }
}
a = new init();
a.displayName()

The first method told me that displayName() is undefined. The way I see it a variable of type Function with name displayName is created, and thus it should work. Any one care to explain why it didn't work?

Answer 1

To create something like a member function you need to add it to the protoype of the constructor function:

function init() {
    this.name = 'Mozilla';
}
init.prototype.displayName = function() {
    alert(this.name);
}

I also highly recommend you to read something about how the object system in JavaScript works. There's a pretty good article about it on MDN: https://developer.mozilla.org/en-US/docs/JavaScript/Introduction_to_Object-Oriented_JavaScript