How to test that a variable is type Map or Array?

Question

In ES6, how can I test if a variable is an Array or a Map?

instance.constructor.name === 'Map' is a risky habit, even if it's core type, doing this with your own class when minified will break the test.

What is the most reliable way to verify that the variable is an instance of Map

Answer 1

const getType = obj => Object.prototype.toString.call(obj).slice(8, -1);

const isArray = obj => getType(obj) === 'Array';

const isMap = obj => getType(obj) === 'Map';


const arr = [];

console.log(isArray(arr)); // true


const map = new Map();

console.log(isMap(map)); // true

Answer 2

Instead of checking the constructor's .name (string) property, just check whether the constructor itself is === Map:

const m = new Map();
console.log(m.constructor === Map);