Get the true type of a variable. Ex: null == "null"

trueTypeOf.js

function trueTypeOf (obj) {
  return {}.toString.call(obj).split(' ')[1].slice(0, -1).toLowerCase();
}

console.log(trueTypeOf()); //undefined
console.log(trueTypeOf(null)); //null
console.log(trueTypeOf(NaN)); //number
console.log(trueTypeOf(5)); //number
console.log(trueTypeOf({})); //object
console.log(trueTypeOf([])); //array
console.log(trueTypeOf('')); //string
console.log(trueTypeOf(function () {})); //function
console.log(trueTypeOf(/a/)); //regexp
console.log(trueTypeOf(new Date())) //date