How to access one object in another object-CodePudding

I am busy creating an object. The end goal is that each evolution will link to a creature in another object.

let fresh = {
  botamon: {
    name: "Botamon",
    image: new URL("https://www.grindosaur.com/img/games/digimon-world/digimon/12-botamon.jpg"),
    stage: "Fresh",
    type: "Data"
  },
}

let inTraining = {
  koromon: {
    name: "Koromon",
    image: new URL("https://www.grindosaur.com/img/games/digimon-world/digimon/50-koromon.jpg"),
    stage: "In-Training",
    type: "Data",
    preDigivolution: fresh.botamon,
    line: rookie.agumon
  },
}

let rookie = {
  agumon: {
    name: "Agumon",
    Image: new URL("https://www.grindosaur.com/img/games/digimon-world/digimon/1-agumon.jpg"),
    Stage: "Rookie",
    Type: "Vaccine",
    PreDigivolution: inTraining.koromon
  },
}

The line: rookie.agumon throws an error, because the way this works is that koromon evolves to agumon so I have no idea why its throwing an error, the error is

digimon-digivolution.js:41 Uncaught ReferenceError: Cannot access 'rookie' before initialization

is it incorrect to call rookie.agumon in the koromon object?

CodePudding user response：

You are trying to resolve an identifier before its declaration. The variable is said to be in a TDZ (temporal dead-zone).

Trying to swap the declaration/initialization statements would still result in a similar ReferenceError: The identifier's resolution would still happen in its TDZ. With just the two statements it is impossible to create a circular reference.

Instead, you can separate the initializations into individual statements as @SebastianSimon suggested, where you assign the references afterwards. Example:

// Initialize separately
const koromon = {/*...*/};
const agumon = {/*...*/};

// Then assign to each other
koromon.digivolution = agumon;
agumon.preDigivolution = koromon;

Or you can use getters to avoid the problem of the TDZ, as @NickParsons suggests. This works because only upon access are we resolving the identifier, at which time we have already left its TDZ. Example:

const koromon = {
  name: "Koromon",
  get digivolution() { return agumon; }
};
const agumon = {
  name: "Agumon",
  get preDigivolution() { return koromon; }
};

console.log("Koromon's digivolution is:", koromon.digivolution.name);