Page 194 - JavaScript

Number.isNaN(NaN); // true
Number.isNaN(0 / 0); // true
Number.isNaN('str' - 12); // true

Number.isNaN(24); // false
Number.isNaN('24'); // false
Number.isNaN(1 / 0); // false
Number.isNaN(Infinity); // false

Number.isNaN('str'); // false
Number.isNaN(undefined); // false
Number.isNaN({}); // false

6

You can check if a value is NaN by comparing it with itself:

value !== value; // true for NaN, false for any other value

You can use the following polyfill for Number.isNaN():

Number.isNaN = Number.isNaN || function(value) {
return value !== value;
}

By contrast, the global function isNaN() returns true not only for NaN, but also for any value or
expression that cannot be coerced into a number:

isNaN(NaN); // true
isNaN(0 / 0); // true
isNaN('str' - 12); // true

isNaN(24); // false
isNaN('24'); // false
isNaN(Infinity); // false

isNaN('str'); // true
isNaN(undefined); // true
isNaN({}); // true

ECMAScript defines a “sameness” algorithm called SameValue which, since ECMAScript 6, can be
invoked with Object.is. Unlike the == and === comparison, using Object.is() will treat NaN as
identical with itself (and -0 as not identical with +0):

Object.is(NaN, NaN) // true
Object.is(+0, 0) // false

NaN === NaN // false
+0 === 0 // true

6

You can use the following polyfill for Object.is() (from MDN):

https://riptutorial.com/ 151