Javascript inheritance, member undefined

Question

I'm making a "class" in a file called Animation.js:

function Animation(s) {
  this.span = s;
};

Animation.prototype = Object.create(Animation.prototype);
Animation.prototype.constructor = Animation;

And I create a child class which is in a file called LinearAnimation.js:

function LinearAnimation(s, cP) {
     Animation.call(s);
     this.controlPoints = cP;
};

LinearAnimation.prototype = Object.create(Animation.prototype);
LinearAnimation.prototype.constructor = LinearAnimation;

The problem is, when I access to this.span member in the LinearAnimation class it says it's undefined. Am I implementing this well? Thank you.

At a glance, you probably want Animation.call(this, s), not Animation.call(s). The first argument to call sets this for the function invocation. — apsillers
– apsillers, Commented Nov 5, 2015 at 19:26
Animation.prototype = Object.create(Animation.prototype); is probably not what you wanted either. — Amit
– Amit, Commented Nov 5, 2015 at 19:26

Amit · Accepted Answer · 2015-11-05 19:31:35Z

5

The Function.prototype.call() function takes a thisArg as it's first argument, meant to be the this inside the called function. After that, any other argument(s) is(are..) passed as input to the called function.

Also, there's no point in replacing the prototype of a function (class) with an object inherited from itself.

Try this:

function Animation(s) {
  this.span = s;
};

function LinearAnimation(s, cP) {
     Animation.call(this, s);
     this.controlPoints = cP;
};
LinearAnimation.prototype = Object.create(Animation.prototype);
LinearAnimation.prototype.constructor = LinearAnimation;

var la = new LinearAnimation('something', [1, 2, 3]);

console.log(la);

answered Nov 5, 2015 at 19:31

Amit

46.5k9 gold badges84 silver badges114 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

apsillers · Accepted Answer · 2015-11-05 19:30:47Z

2

You want Animation.call(this, s), not Animation.call(s). The first argument to call sets this for the function invocation. In your code, you're calling Animation with a this of s, so your s argument gets a span property, rather than the this being constructed in LinearAniamtion.

answered Nov 5, 2015 at 19:30

apsillers

117k18 gold badges248 silver badges249 bronze badges

Collectives™ on Stack Overflow

Javascript inheritance, member undefined

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related