Try splitting on a regex that matches spaces or hyphens and taking the last element:
var lastWord = function(o) {
return (""+o).replace(/[s-]+$/,'').split(/[s-]/).pop();
};
lastWord('This is a test.'); // => 'test.'
lastWord('Here is something to-do.'); // => 'do.'
As @alex points out, it's worth trimming any trailing whitespace or hyphens. Ensuring the argument is a string is a good idea too.
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