JS NaN
NaN is a Number value representing an invalid numeric result. It is not equal to itself.
Where to run this
This example uses the JavaScript console playground. Select Run to execute it; the example does not run on this lesson page.
A practical example
const quantity = Number("several");
console.log(Number.isNaN(quantity));
console.log(quantity === NaN);
What happens
The checks produce true and false.