how to check isnan in javascript code example

Example 1: compare NaN in javascript if condititon

// Use isNaN() 
// In javascript compare NaN direct alweys return false
let num1 = Number("Vishal");

// This code never work
if(num1 == NaN){  // Direct compare NaN alweys return false so use isNaN() function
  ....... Your Code .......
}  

// This code work
if(isNaN(num1){
  .........Your Code .......
}

Example 2: isnan in javascript

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

Example 3: javascript check if is nan

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

Example 4: isNaN javascript

var j ="Hello World" // isNaN (j) returns true
  var n = 15; // isNaN (n) returns false

  if(isNaN(n) == true)   // NaN means >> Not a Number
  {
      console.log("yes, it's a string");
  }
  else
  {
      console.log("no, it's a number");
  }