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JavaScript JavaScript Functions Arrow Functions Testing for Number Arguments

nasser mohammed
nasser mohammed
13,160 Points

Testing for Number Arguments Pass a string argument

Hi. When I pass a string argument like '10', the function not work well, either when I did the testing.

const getRandom = (lower, upper) => {
  if (isNaN(lower) || isNaN(upper)) { 
  document.querySelector('main').innerHTML = `<h2>The 2 values should be numbers</h2>`;
  } else {
    const random = Math.floor(Math.random() * (upper - lower + 1)) + lower;
  const main = document.querySelector('main').innerHTML = `<h2>${random} is a random number between ${lower} and ${upper}<h2>`;
  return main;


the result is: 310 is a random number between 10 and 40

1 Answer

Travis Alstrand
Travis Alstrand
Treehouse Teacher

You can see in the docs here it says ... "The isNaN() function determines whether a value is NaN when converted to a number. Because coercion inside the isNaN() function can be surprising, you may alternatively want to use Number.isNaN()."

So it's taking your string of '10' and returning true after converting it to a number.