Gorynych, please remove the solution from the comment, it's already available in the Solutions section. Thanks.

Sorry for late reply. You are not returning anything from array_diff, which is why you're getting the error.

Unfortunately, I can't edit either.

What are you returning from array_diff function?

This crash is possible if you return undefined. I can't edit the test cases anymore, sorry.

Thanks - you're both right, I've corrected the second code example.

Awesome solution, it convinces me to change the category to Reference.

Great kata! And I would keep the low timeouts, forces an efficient solution

Thanks jhoffner!

I agree with Icefox, I also do not understand why a single word is a special case.

For example:

truncate('This is my testing function what is it going to do.',3) # returns "This..."'
truncate('Thisismytestingfunction.',10) # returns 'Thisismytes...'
truncate('Thisismytestingfunction omg.',10) # returns 'Thisismytestingfunction'

Shouldn't the first word, which is longer than the limit also be truncated?

I'm a bit confused, whenever I run the code (even with an empty method), I get "NoMethodError: undefined method `+' for 0:Fixnum".

Could you help?

This page explains well what is going in in Array#reduce: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce

I originally had a line like that:

return false if string.length.even?

but I passed. This is of course wrong, but it would be cool to have a test for this. Could you add a test with an even palindrome?