typeof

The typeof operator returns the type of a variable or an expression

                var luna = {};
                var lunaPink = function(){};
                document.getElementById("demo").innerHTML =
                typeof "" + "
" +
                typeof "John" + "
" +
                typeof luna + "
" +
                typeof lunaPink;
                

網頁放一個id為demo的元素，即可以看出效果

結果將渲染為：
string
string
object
function