Page 165 - JavaScript

// The one and only
Number.isNaN(NaN); // true

// Numbers
Number.isNaN(1); // false
Number.isNaN(-2e-4); // false
Number.isNaN(Infinity); // false

// Values not of type number
Number.isNaN(true); // false
Number.isNaN(false); // false
Number.isNaN(null); // false
Number.isNaN(""); // false
Number.isNaN(" "); // false
Number.isNaN("45.3"); // false
Number.isNaN("1.2e3"); // false
Number.isNaN("Infinity"); // false
Number.isNaN(new Date); // false
Number.isNaN("10$"); // false
Number.isNaN("hello"); // false
Number.isNaN(undefined); // false
Number.isNaN(); // false
Number.isNaN(function(){}); // false
Number.isNaN({}); // false
Number.isNaN([]); // false
Number.isNaN([1]); // false
Number.isNaN([1, 2]); // false
Number.isNaN([true]); // false

null

null is used for representing the intentional absence of an object value and is a primitive value.
Unlike undefined, it is not a property of the global object.

It is equal to undefined but not identical to it.

null == undefined; // true
null === undefined; // false

CAREFUL: The typeof null is 'object'.

typeof null; // 'object';

To properly check if a value is null, compare it with the strict equality operator

var a = null;

a === null; // true

undefined and null

At first glance it may appear that null and undefined are basically the same, however there are
subtle but important differences.

https://riptutorial.com/ 122