Installation

Install the package using npm:

npm install is-negative-nan

Or using yarn:

yarn add is-negative-nan

Or using pnpm:

pnpm add is-negative-nan

Usage

import { isNegativeNaN } from 'is-negative-nan';

console.log(isNegativeNaN(-NaN)); // true

Why is this useful?

console.log(NaN === NaN); // false
console.log(-NaN === NaN); // false

NaN; // NaN
-NaN; // NaN

String(NaN); // 'NaN'
String(-NaN); // 'NaN'

Number.isNaN(NaN); // true
Number.isNaN(-NaN); // true

Object.is(NaN, NaN); // true
Object.is(-NaN, NaN); // true
Object.is(-NaN, -NaN); // true
Object.is(NaN, -NaN); // true

How it works?

isNegativeNaN converts the number to a Float64Array and then to a Uint32Array. It then checks if the number is negative by checking the 31st bit of the Uint32Array.

export function isNegativeNaN(val: number) {
  if (!Number.isNaN(val)) return false;
  const f64 = new Float64Array(1);
  f64[0] = val;
  const u32 = new Uint32Array(f64.buffer);
  const isNegative = u32[1] >>> 31 === 1;

  return isNegative;
}