js value is NaN code example

Example 1: isnan in javascript

var s = userInput[0];
  if(isNaN(s) !== true)
  {
      console.log("yes");
  }
  else
  {
      console.log("no");
  }

Example 2: javascript check if is nan

function isNaN(x) {
   return x !== x;
};
isNaN(NaN);//true