<script type=text/javascript>   

function saveName (firstName) {

    function capitalizeName () {

        return firstName.toUpperCase();

    }

    var capitalized = capitalizeName();console.log(capitalized instanceof String);

    return capitalized; 

}

console.log(saveName(Robert)); // Returns ROBERT

</script>

Question:

I want to check the type of capitalized , so I use capitalized instanceof String? But it shows: false in console, I do not want to try capitalized instanceof Function, Object...It will take too much time, so what is the best way to detect a variable type?