JavaScript - Child objects called by functions to update child objects

Question

I am learning about objects and their scopes, I got confused and decided to make a D&D pathfinder character sheet for practice.

I made the character sheet as an object, child objects for ability scores, strength/dexterity/intelligence/etc... and then base and modifier values.

in D&D you use your base value to calculate your modifier value and the modifier is used throughout the game. The calculation for modifier is (base - 10) / 2

as i run this i only get 0 when called console.log(characterSheet.abilityScore.strength.modifier)

I assume my confusion is about my understanding of the scope range between the function and modifier/base. but I'm not sure where to start.

const characterSheet = {
  abilityScore: {
    strength: {
      base: 2,
      modifier: 0,
      calcMod: function () {
        this.modifier = Math.floor((this.base - 10) / 2);
      },
    },
    dexterity: {
      base: 8,
      modifier: 0,
      calcMod: function () {
        this.modifier = Math.floor((this.base - 10) / 2);
      },
    },
    intelligence: {
      base: 16,
      modifier: 0,
      calcMod: function () {
        this.modifier = Math.floor((this.base - 10) / 2);
      },
    },
  },
}

I have also tried placing the function in the global scope but always returns NaN.

const characterSheet = {
  abilityScore: {
    strength: {
      base: 2,
      modifier: function () {
        return calcMod(this.base);
      },
    strength: {
      base: 8,
      modifier: function () {
        return calcMod(this.base);
      },
    },
    strength: {
      base: 16,
      modifier: function () {
        return calcMod(this.base);
      },
    },
  },
}};
function calcMod(val) {
  return Math.floor((val - 10) / 2);
}

console.log(calcMod(characterSheet.abilityScore.strength));

After I call `characterSheet.abilityScore.strength.calcMod()`, when I log `characterSheet.abilityScore.strength.modifier` it shows `-4`. — Barmar, Sep 29 '22 at 00:38
@MisterJojo I was referencing for when I make a function outside the object. — mastaSabin, Sep 29 '22 at 01:05
@Barmar am I building this wrong then? I don't want to call the function every time I want to call the modifier. wouldn't that be repeating myself? — mastaSabin, Sep 29 '22 at 01:08
@mastaSabin Please [edit] your question to show the code where you make the function "outside the object". — Bergi, Sep 29 '22 at 01:10
@mastaSabin If you don't want to repeat yourself, use one function that builds these objects: `{strength: buildScore(2), dexterity: buildScore(8), intelligence: buildScore(16)}` — Bergi, Sep 29 '22 at 01:12
@MisterJojo updated to include function outside of the object. also, do you mean pathfinder? It's D&D 3.6 basically — mastaSabin, Sep 29 '22 at 01:26
I don't know what is `D&D 3.6` is there a link which can explain this stuff? — Mister Jojo, Sep 29 '22 at 01:29
@MisterJojo Doungens and Dragons https://dnd.wizards.com though I don't know if pathfinder is part of the Wizards company or not. I am referencing https://www.d20pfsrd.com/ for most of my info about pathfinder. — mastaSabin, Sep 29 '22 at 01:31
change `console.log(calcMod(characterSheet.abilityScore.strength));` to `console.log(calcMod(characterSheet.abilityScore.strength.base));` — Mister Jojo, Sep 29 '22 at 01:40
ok, D&D stands for Dungeons and Dragons... I hardly play any games (I didn't even know what a sudoku was recently), next time try to conceive that everyone does not gravitate in the same universe as yours ;) — Mister Jojo, Sep 29 '22 at 01:48
@MisterJojo I was mostly trying to keep the details related to JavaScript. — mastaSabin, Sep 29 '22 at 02:36
@Bergi how could I build this function? when I use it as you suggest it works as expected. but when i place modifier: `buildScore(this.base)` it returns NaN. — mastaSabin, Sep 29 '22 at 02:46
Yes, you are supposed to use it as I suggested. It's still not clear what other way you want? — Bergi, Sep 29 '22 at 02:49

Mister Jojo · Accepted Answer · 2022-09-29T02:59:46.633

1

you can use that... ?

const characterSheet =
  { abilityScore: 
    { strength:
      { base      : 2
      , modifier  : 0
      }
    , dexterity: 
      { base      : 8
      , modifier  : 0
      }
    , intelligence: 
      { base      : 16
      , modifier  : 0
      }
    , calcMod ( ability )
      { 
      return this[ability].modifier = 0 | ((this[ability].base - 10) / 2);       
  } } } 

console.log( characterSheet.abilityScore.calcMod( 'strength' ) )

console.log( characterSheet.abilityScore.strength.modifier )

OR:

const characterSheet =
  { abilityScore: 
    { strength     : { base :  2, modifier : 0 }
    , dexterity    : { base :  8, modifier : 0 }
    , intelligence : { base : 16, modifier : 0 }
  } };
  
function calcMod( val ) 
  {
  return val.modifier = 0 | ((val.base - 10) / 2);
  }

console.log( calcMod( characterSheet.abilityScore.strength ))

edited Sep 29 '22 at 02:59

answered Sep 29 '22 at 02:02

Mister Jojo

20,093
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is that an or operator? `|` – mastaSabin Sep 29 '22 at 06:12
@mastaSabin No, it's a [more concise alternative to `Math.floor`](https://stackoverflow.com/q/7487977/1048572) which doesn't work properly for large numbers. I wouldn't recommend it. – Bergi Sep 29 '22 at 07:52
cool! thanks for the explination. – mastaSabin Sep 29 '22 at 08:40

score 1 · Answer 2 · answered Sep 29 '22 at 02:53

1

You should use

function buildScore(base) {
  return {
    base,
    modifier: Math.floor((base - 10) / 2),
  };
}
const characterSheet = {
  abilityScore: {
    strength: buildScore(2),
    dexterity: buildScore(8),
    intelligence: buildScore(16),
  },
};

console.log(characterSheet.abilityScore.strength);

No methods, no problems. You could also achieve something like this with getters, but it would be much more complicated.

answered Sep 29 '22 at 02:53

Bergi

630,263
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957
1,375

ohh that looks pretty. I'll try that out now. – mastaSabin Sep 29 '22 at 06:13

score 0 · Answer 3 · answered Sep 29 '22 at 13:57

You can use a getter for modifier that calls calcMod(). This calls a function to return the value of the property, so it can calculate it based on the current value of this.base.

function calcMod(val) {
  return Math.floor((val - 10) / 2);
}

const characterSheet = {
  abilityScore: {
    strength: {
      base: 2,
      get modifier() {
        return calcMod(this.base);
      }
    },
    dexterity: {
      base: 8,
      get modifier() {
        return calcMod(this.base);
      }
    },
    intelligence: {
      base: 16,
      get modifier() {
        return calcMod(this.base);
      }
    },
  },
}

console.log(characterSheet.abilityScore.dexterity.modifier);
characterSheet.abilityScore.dexterity.base = 10;
console.log(characterSheet.abilityScore.dexterity.modifier);

JavaScript - Child objects called by functions to update child objects

3 Answers3