JS: global isNaN

isNaN is the value of the property key "isNaN" of the Global Object.

console.assert(globalThis["isNaN"] === isNaN);

isNaN(arg)

Converts arg to number first, and return true if it is NaN, else, false. 〔see NaN〕

console.assert(isNaN(NaN));
console.assert(isNaN("NaN"));
console.assert(isNaN("3") === false);
console.assert(isNaN(3) === false);
console.assert(isNaN(Infinity) === false);