How do I pass ES6 default parameters from a subclass to its superclass?

Question

I've got this code:

class Plant {
  constructor({name = 'General Plant', height = 0, depth = 1, age = 0}) {
    this.name = name;
    this.stats = {
      height: height,
      depth: depth,
      age: age
    };
  }
}

class Bush extends Plant {
  constructor({name = 'General Bush', height = 2, depth = 2}) {
    super(arguments)
  }
}

But calling myBush = new Bush({}) results in an object with the name "General Plant" instead of "General Bush". Is there any way to set the default values in the subclass without having to manually call this.name = name in the constructor?

I know that when I'm calling `super(arguments)` that it's the raw arguments supplied to `new Bush`. I'm wanting to know if there's a way I can pass the arguments that have been modified. — Andrew, May 08 '17 at 20:43

Bergi · Accepted Answer · 2017-05-08T20:59:58.247

4

Default initialisers don't mutate the arguments object (such happened only in ye olde sloppy mode).
You need to pass the actual values from the parameter variables:

class Bush extends Plant {
  constructor({name = 'General Bush', height = 2, depth = 2, age}) {
    super({name, height, depth, age});
  }
}

Alternatively (but with different behaviour for undefined values and surplus properties) you might employ Object.assign:

class Bush extends Plant {
  constructor(opts) {
    super(Object.assign({name: 'General Bush', height: 2, depth: 2}, opts));
  }
}

edited May 08 '17 at 20:59

answered May 08 '17 at 20:47

Bergi

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So, if I'm too lazy to write the name of a variable more than once (which I am), then I'd have to give up on using the cool new ES6 default parameters and manually extend the arguments like this: `constructor(){ super($.extend(arguments, { name: 'General Bush', ... }) }`? – Andrew May 08 '17 at 20:52
Variables are only introduced to use them more than once :-) Notice that `$.extend` (or better `Object.assign`) has slightly different semantics than default intialisers. – Bergi May 08 '17 at 20:56
Yeah, I just now realized I should've used `Object.assign` in my example. Still used to old fashioned jQuery filling in the holes of ES5. I figured I'd have to give up on using default parameters for constructors since the way I have it setup still errors out when you call `new Bush()` without an object. – Andrew May 08 '17 at 21:00
@Andrew For that, you need [a default `= {}` for the whole parameter](http://stackoverflow.com/a/41108626/1048572) – Bergi May 08 '17 at 21:02
Apparently not. this works perfectly: `constructor() { super(Object.assign({name: 'General Bush', height: 2, depth: 2}, ...arguments)) }` – Andrew May 08 '17 at 21:38
I meant you need it when you don't want to give up on default parameters :-) – Bergi May 08 '17 at 21:39

How do I pass ES6 default parameters from a subclass to its superclass?

1 Answers1