One side of your logical expression was not a comparison, so the overall condition would be true based on the value of the "lower" argument. But to fix that, and to account for "isNaN" being a function, you could perform your test like this instead:

 if ( isNaN(lower) || isNaN(upper) ) {

I notice 2 issues with your code.

1)

You don't want to check if lower or upper are === to isNaN, because isNaN is a function which determines whether the argument you enter is not a number. You want that part of your code to look like this: if (isNaN(lower) || isNaN(upper))

2)

You are missing a semi-colon after your return random. That part of your code should look like this: return random;

The complete code should look more like this:

function getRandomNumber(lower,upper) { if (isNaN(lower) || isNaN(upper)) { throw new Error("Please enter a number"); } var random = Math.floor(Math.random() * (upper - lower + 1)) + lower; return random; }

Also in order to get a better idea of what's going on in your code (debugging) try using console.log() in every area of your code where it should be outputting.