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Kevin Powell - Community•3d ago

super()

Hey, am i using super() correctly in this case? I had a bit a trouble understanding the functionality.

class Animal {
  constructor(species) {
    this.species = species
  }
  get Species() {
    return this.species
  }
}

class Spider extends Animal {
  constructor(species, type) {
    super(species)
    this.type = type
  }
  get SpeciesReason() {
    return `I'm an ${this.species} because I have 8 legs.`
  }
}

let spider = new Spider("Arachnid", "House Spider");

class Animal {
  constructor(species) {
    this.species = species
  }
  get Species() {
    return this.species
  }
}

class Spider extends Animal {
  constructor(species, type) {
    super(species)
    this.type = type
  }
  get SpeciesReason() {
    return `I'm an ${this.species} because I have 8 legs.`
  }
}

let spider = new Spider("Arachnid", "House Spider");

I've played around with it and found the following which makes me think that i'm doing everything right as it works, but i might be wrong. 1) If i don't include super() and species in the constructor args for the Spider class, since it has it's own constructor it throws an error saying must call super constructor before using 'this' in derived class constructor as i'm trying to use this.species. 2) If i don't include species in the constructor args but have a super(species) it throws an error saying species isn't defined. 3) If i include species in the constructor args but don't include super(species) it throws an error saying must call super constructor before using 'this' in derived class constructor. I'd appreciate any insight. Thanks in advance.

33 Replies

ἔρως•3d ago

you didn't define the public property species in the class Animal you also didn't define type in Spider calling super is mandatory - no way around it unless EVERYTHING is static

snxxwyy•3d ago

i know, i was checking if i was using it correctly?

ἔρως•3d ago

which is not what you want you are, yes

snxxwyy•3d ago

also i'm confused about the first two things you said, are you saying those in reference to the errors, or are they just general things i'm not doing? oh cool, glad i got that down

ἔρως•3d ago

both

snxxwyy•3d ago

oh so i need to do this?

class Animal {
  species;

  constructor(species) {
    this.species = species
  }
  get Species() {
    return this.species
  }
}

class Animal {
  species;

  constructor(species) {
    this.species = species
  }
  get Species() {
    return this.species
  }
}

and then the same for type in Spider?

ἔρως•3d ago

no

snxxwyy•3d ago

oh?

ἔρως•3d ago

inside the class

snxxwyy•3d ago

oh yeah just changed that haha realised just then okay so if it's inside the class, then like that?

ἔρως•3d ago

yes, like that

snxxwyy•3d ago

okay cool, thanks for the clarification on everything

ἔρως•3d ago

this.species <-- this also shouldn't exist, as far as i know no, it works

snxxwyy•3d ago

sorry, what do you mean?

ἔρως•3d ago

🤔

snxxwyy•3d ago

oh okay why did you think it wouldn't?

ἔρως•3d ago

because, usually, you use super to access those

snxxwyy•3d ago

like super.species?

ἔρως•3d ago

yeah

snxxwyy•3d ago

yeah i've seen that as well

ἔρως•3d ago

but if it works, then it works

snxxwyy•3d ago

do you think it's recommended to use super.species to be safe? or as a more general thing, super.xyz if you're using a value from a parent class?

ἔρως•3d ago

i don't know why but it doesn't work 🤔

snxxwyy•3d ago

also a quick question regarding this. What would happen if i didn't include species; at the top? The only thing i could think of is that it wouldn't allow you to change it to a private property with # if you wanted.

ἔρως•3d ago

if you try to access the value before this.species, it wouldn't exist

snxxwyy•3d ago

does it say it's undefined for you when you do that?

ἔρως•3d ago

yes with super.species

snxxwyy•3d ago

yeah that's the same here did they perhaps change the way it works?

ἔρως•3d ago

no, but i might have misunderstood it

snxxwyy•3d ago

oh okay so if i tried to access it before i defined it in the constructor it wouldn't exist?

ἔρως•3d ago

exactly

snxxwyy•3d ago

ah okay i see thank for your help

ἔρως•3d ago

you're welcome

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