isArray equivalent for new Map()?

Question

How can I determine that my data structure is of type Map()?

I've been looking everywhere, and can't find any method

I really want to get into using them because I can use objects as keys!

Answer 1

You can use the instanceof opeartor

var map = new Map();
var arr = [];

console.log(map instanceof Map);
console.log(map instanceof Array);
console.log(arr instanceof Map);
console.log(arr instanceof Array);

From the Documentation

The instanceof operator tests whether an object has in its prototype chain the prototype property of a constructor.

Answer 2

You could use either instanceof operator or the constructor property and check against the object.

For more information read this: What's the difference between using instanceof and checking the constructor?

var map = new Map();
var arr = [];

console.log(map instanceof Map);         // true
console.log(map instanceof Array);       // false
console.log(map.constructor === Map);    // true
console.log(map.constructor === Array);  // false

console.log(arr instanceof Map);         // false
console.log(arr instanceof Array);       // true
console.log(arr.constructor === Map);    // false
console.log(arr.constructor === Array);  // true

// caveat!
console.log(arr.constructor === Object); // false
console.log(map.constructor === Object); // false
console.log(arr instanceof Object);      // true
console.log(map instanceof Object);      // true

Answer 3

You can even use Object.prototype.toString.call, though instanceof(@suren srapyan's answer) is more preferred

var a = [1,2,3];
var m = new Map()
a.forEach((x,i)=>m.set(i+1, x));

console.log(Object.prototype.toString.call(m))