I don't consider something like: function is_empty(obj){if(obj instanceof Array){return obj.length===0;}else if(obj instanceof Object){for(var i in obj)return

I don't consider something like: function is_empty(obj){if(obj instanceof Array){return obj.length===0;}else if(obj instanceof Object){for(var i in obj)return false;return true;}else return !obj; to be a one-liner simply because it was crammed into one line.