JavaScript: new objects of the same class as keys for a dictionary

February 1, 2024

I tried the following, but the dictionary only had one key.

class dog
{
}
dic = {}

for(let i=0; i<3; i++)
{
    dic[new dog()] = i;
}

for(var item in dic)
{
 console.log(dic[item]);
}

But that was not what I intended. I wanted it to work like the following C# code, whose output is 0 1 2. It seems that each new dog() in the JS code above is treated as the same object and thus the value overwrites the previous one. How can I modify the JS code so that it work like the C# code below?

using System;
using System.Collections.Generic;

class dog
{
}

public class Program
{
    public static void Main()
    {
        var dic = new Dictionary<object,int>();

        for(var i=0; i<3; i++)
        {
            dic[new dog()] = i;
        }
        
        foreach(var item in dic.Keys)
        {
          Console.WriteLine(dic[item]);
        }
    }
}

>Solution :

Object keys can only be one of two type i.e. Strings or Symbols. To achieve the desired behaviour, you can use a Map instead of an object as a dictionary.

class Dog {
}

const map = new Map();

for (let i = 0; i < 3; i++) {
    map.set(new Dog(), i);
}

for (const [key, value] of map.entries()) {
    console.log(value);
}