Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

JavaScript JavaScript Numbers The Math Object Random Number Challenge – Solution

Posted by frank din
.a{fill-rule:evenodd;}techdegree
frank din
Full Stack JavaScript Techdegree Student 1,381 Points

How do you determine if a value is not a number?

I'm trying to add an error message in case the user typed a value that was not a number, but I can't find a way to detect if a value is a number or not? const userUpperLim = +prompt(Type an upper limit); if (userUpperLim === NaN){ alert(please type proper number); } else{ alert(userUpperLim is good); }

I tried this but it skips right over the if statement and goes to the else statement.

Casey Beaver
Casey Beaver
5,619 Points

let userUpperLim = prompt("Type an upper limit.");

if ( isNaN( userUpperLim )) { userUpperLim = alert("Please type a proper number."); } else { alert("userUpperLim is good."); }

2 Answers

Martin Sole
Martin Sole
82,199 Points
Martin Sole
Martin Sole
82,199 Points

Hi

You can also use typeof which checks a values type. So for your example it could be used as

if (typeof userUpperLim !== 'number')

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof

furkan
furkan
11,733 Points
furkan
furkan
11,733 Points

Hey there,

Have a look at this link, might help:

https://www.w3schools.com/jsref/jsref_isnan.asp