Why does the NaN gets printed in the console?

Tell us what’s happening:

Your code so far

function bouncer(arr) {
  let emparr = [];
  // Don't show a false ID to this bouncer.
  for (let i=0; i<arr.length; i++){
      case false:
      case null:
      case 0:
      case "":
      case NaN:
      case undefined: 

  return emparr;

console.log(bouncer([1, null, NaN, 2, undefined]));

Because NaN !== NaN

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NaN === NaN is false

You need to find a different way to solve this. Consider this, these are all falsy values so with these value == false is true (note the not-strict equality operator)

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.filter() removes any value that is false.
All your case statements evaluate to false.
So just return the value inside a .filter() method.

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