How to check if object of type map - JavaScript

In this article we will learn how to check if object of type map in JavaScript.

It is very common to check if object of type map in JavaScript in JavaScript.

Problem

Now we have a problem which is that we want to check if object of type map.

Imagine we have map like this:

const map = new Map([
    ['name', 'John'],
    ['age', 30]
]);

And we want to check if this object is typeof map or not.

How to solve this problem?

Use the instanceof operator to check if an object is a Map, e.g. myObj instanceof map.

Solution:

The instanceof operator returns true if the prototype property of a constructor appears in the prototype chain otherwise returns false.

Let's see an example

// map
const map = new Map([
    ['name', 'John'],
    ['age', 30]
]);

// Tests:
console.log(map instanceof Map);
console.log('map' instanceof Map);
console.log(new Map() instanceof Map);
console.log({} instanceof Map);

Output

true
false
false
false

This approach would also work if you extend the Map class.

class CustomMap extends Map {
  example() {
    console.log('Do something');
  }
}

const map = new CustomMap();

// Tests:
console.log(map instanceof Map); // true
console.log(new Map([1, 2, 3]) instanceof Map); // true
console.log(new Set() instanceof Map); // false
console.log({} instanceof Map); // false

Output

true
true
false
false

Thank you for reading

Thank you for reading my blog. 🚀