'How to make an analogue of Array.isArray() for Map in JS?

I'm researching prototypes in JS.

Please tell me how to add the Map.isMap(object) function to the Map prototype.

I was able to make object.isMap() by code:

Map.prototype.isMap = function() {
  return this.__proto__.toString().toLowerCase().includes("map");
}

I know editing prototype chain is a bad practice in JS. What is the best way to create such function?

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