Number.NaN

The Number.NaN property represents Not-A-Number. Equivalent of NaN.

You do not have to create a Number object to access this static property (use Number.NaN).

function sanitise(x) {
  if (isNaN(x)) {
    return Number.NaN;
  }
  return x;
}

See Testing against NaN on the NaN page.

• The global NaN object.
• The Number object it belongs to.