cjsp2

yesindexing.js

class Indexable {
  constructor(){
    this._indexer = Symbol();
  }
  [Symbol.toPrimitive](){ return this._indexer }
}

class Animal extends Indexable {}

const cat = new Animal();
const dog = new Animal();

const talk = {
  [cat]: 'meow',
  [dog]: 'woof'
};

console.log(talk[cat]); // "meow", hooray!!!
console.log(talk[dog]); // "woof"