I'm confused by your question, hksong. My solution does indeed handle '(hello)' properly:

$ ./validBraces2.js '(hello)'
Valid braces?: true
$ ./validBraces2.js '(hello)]'
Valid braces?: false
$ ./validBraces2.js '[(hello)]'
Valid braces?: true

What are you seeing that I am not?

What was the point of even bringing it up when your solution would fail as well?

Note that reducers are supposed to be pure--they are not allowed to modify r or its contents, so you should be returning new objects every time you modify them.

All input strings will be nonempty, and will only consist of parentheses, brackets and curly braces: ()[]{}

It does what is asked, so it's fine by me at least.

This solution will fail if there's anything other than a brace-y kind of thing in between the parens (e.g. "(hello)"), so it's not very realistic.

See the follow-up submission for a more efficient solution.