I agree it's concise, but I don't get why people vote this as best practice.

would and should;-)... l and r are global values, so should be never best practice...

This would fail if there were any characters other than "?" or "!" in the string. And double equals should never be best practice.

Thanks;-)!

very nice

thanks for the info myjinxin2015.

Thanks;-)... haven't seen the question...

[...string] equals to string.split("")

the 0 at the end of reduce means initialValue. If you omit it, the function will choose the first element as the initialvalue, i.e left[0], right[0]