How to detect a invalid prompt answer?

Question

Example of what I am trying to achieve:

 var p = prompt("What is your favorite number?", 1, 2, 3, 4); if (p) { function checkForInvalid() { const invalid = "invalid" } } if (p === invalid) { alert("Sorry, I don't know that number"); }

or something similar. I am relatively new to javascript. Could I use a function to check if the number is not specified within the prompt? I am not trying to validate anything...

Answer 1

 const validNumbers = [1,2,3,4]; var p = prompt("What is your favorite number?", validNumbers[0]); if (validNumbers.indexOf(Number(p)) == -1) { alert("Sorry, I don't know that number"); }