Welcome to the Treehouse Community

The Treehouse Community is a meeting place for developers, designers, and programmers of all backgrounds and skill levels to get support. Collaborate here on code errors or bugs that you need feedback on, or asking for an extra set of eyes on your latest project. Join thousands of Treehouse students and alumni in the community today. (Note: Only Treehouse students can comment or ask questions, but non-students are welcome to browse our conversations.)

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and a supportive community. Start your free trial today.

JavaScript Object-Oriented JavaScript (2015) Introduction to Methods Adding a Method to an Object

Michael Zeltner
Michael Zeltner
128 Points

"Undefined" in Console

Why is there "undefined" logged into the the console and how can you prevent this?

If a function doesn't return a value, then it will return undefined (https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/undefined).

Don't worry about preventing it as it's not necessarily a bad thing. For example, if the function in question is a mutator that doesn't need to return a value then so be it.

1 Answer

Steven Parker
Steven Parker
218,583 Points

If you're just firing off functions from the console, it is normal for the console to show you the return value (or "undefined" if there isn't any) as Evans observed.

You can prevent this by adding a return statement to any function you plan on using this way. If the function has no other reason to return a value, you could do something specifically for the console such as returning a string with the function name followed by the word "done".