is-it-NaN-or-not.js

const mightBeNaN = NaN // NaN means "Not-a-Number"

// Anything compares false when compared to NaN:
console.log(37 === NaN) // false
console.log(mightBeNaN === NaN) // false

// NaN is the only value that does not equal itself:
console.log(mightBeNaN !== mightBeNaN) // true

// Creating an invalid Date results in the value NaN:
console.log(new Date(`invalid`) !== new Date(`invalid`)) // true

// For improved code readability, some developers prefer Number.isNan():
console.log(Number.isNan(mightBeNaN)) // true