Check if a number is negative

const isNegative = (n) => Math.sign(n) === -1;

// Or
const isNegative = (n) => n < 0;

const isNegative = (n: number): boolean => Math.sign(n) === -1;

// Or
const isNegative = (n: number): boolean => n < 0;

isNegative(-3); // true
isNegative(8); // false