function isFibonacci(n) {
  var fib,
    a = (5 * Math.pow(n, 2) + 4),
    b = (5 * Math.pow(n, 2) - 4)

  var result = Math.sqrt(a) % 1 == 0,
    res = Math.sqrt(b) % 1 == 0;

  //fixed this line
  if (result || res == true) // checks the given input is fibonacci series
  {
    fib = Math.round(n * 1.618); // finds the next fibonacci series of given input
    console.log("The next Fibonacci number is " + fib);

  } else {
    console.log(`The given number ${n} is not a fibonacci number`);
  }
}

$('#fib').on("keyup change", function() {
  isFibonacci(+this.value)
})