Add safeguards in onTab

[ArsalanDotMe]

Checks for undefined before calling focus() on an element

I'm facing a problem in my React app that uses fullpage.js. Whenever I press the Tab key, the keydown handler inside fullPage fails and prevents my own keydown handlers to work. In this pull request, I added a simple check that prevents calling .focus() on undefined.

[alvarotrigo]

Awesome! Thanks for the fix! Didn't notice the bug!
Could you please add the return statement within the condition? Then I'll merge it!

[alvarotrigo]

Missing the return statement here inside the condtion.

[ArsalanDotMe]

I omitted the return statement inside the condition because regardless of whether the firstFocusableElement was defined or not, we MUST return. Adding the return statement inside the condition would make it have 2 return statements. Just FYI

[alvarotrigo]

Right now you are always returning undefined.
But we need to return the focusable element if we don't want to break the code :)

See a few lines ahead this variable assign:

activeElement = preventAndFocusFirst(e);

[ArsalanDotMe]

Ah yes, I get that now. I'll make the change.

[alvarotrigo]

If you want to keep a single return, probaby easier something like this:

return firstFocusableElement ? firstFocusableElement.focus() : null;

[ArsalanDotMe]

made the change for a single return statement while returning the focused element if present.

[alvarotrigo]

Thanks! Merged!