CODEWITHSUNDEEP
javascriptoopinheritance
cantaboop
cantaboop

Reputation: 11

Why does this example of inheritance not work on my computer?

I have some Java background but now I am trying to write some simple games in JavaScript and HTML. I'm struggling to understand how OOP works because it seems like there are different ways of creating objects? I wrote this snippet referencing a friend's code but the console gives me "uncaught TypeError: Cannot set property 'roar' of undefined". Why does the code work for him but not for me? Is he running some kind of server side library?

test.js:

function Animal() {

    this.needsAir = true;

    this.roar = function() {

        console.log("roar");    

    }

}

function Bear() {

    Animal.call();

}

var init = function() {

    var bear = new Bear();
    bear.roar();
    console.log(bear.needsAir)

}

index.html: 

<html>
    <head>
        <script type="text/javascript" src="./test.js"></script>
    </head>
    <body>
        <script type="text/javascript">
            window.onload = function() {
                    init();
            }
        </script>
    </body>
</html>

Upvotes: 0

Views: 39

Answers (3)

Sachin
Sachin

Reputation: 978

your Bear function needs to pass this to Animal call.

To understand javascript inheritance better you can check out this blog on understanding javascript inheritance

Upvotes: 0

Soren
Soren

Reputation: 14688

Your functions have different this -- try to use the apply methods, which would get you somewhat further, like;

function Bear() {
    Animal.apply(this);
}

There are a lot more in javascript which is needed, such as prototype definitions

Upvotes: 0

Daniel A. White
Daniel A. White

Reputation: 190941

You need to pass this to .call.

function Bear() {

    Animal.call(this);

}

Also, your prototype inheritance isn't complete as well.

Upvotes: 6

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