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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
228,978 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".