Javascript - How to get the size in bytes of a Map

Question

How can I get the size in bytes of the following Map?

const cache = new Map();
cache.set("1", { id: "1" });

Answer 1

Map object does not define default stringification, that is, JSON.stringify will not work on it by default, nor mapObj.toString() will return a meaningful answer. Therefore, you need to define how to turn a Map to a string, so that you can estimate its size.

Building on this great answer:

function mapSize(oMap){
    function replacer(key, value) {
      if(value instanceof Map) {
        return {
          dataType: 'Map',
          value: [...value],
        };
      } else {
        return value;
      }
    }
    return JSON.stringify(oMap, replacer).length;
}

let test= new Map([["a",2],["b",3]]);
console.log(mapSize(test)); //44

This will return something you can use to approximate. Beware that 'dataType' and 'value' fields are arbitrary, and they effect the 'size'.