getClass method

function getClass(o) {
    var res;
    return o == null
      ? o === null ? "null" : "undefined"
      : (res = o.constructor
                .toString()
                .match(/^function ([^\(]+)|object (\w+)/))
        && res[1] || res[2];
}

function assertEquals(a,b) {
  a === b
    ? console.log(a,"and", b, "are equal.")
    : console.error(a, "and", b, " are not equal.");
}

assertEquals(getClass(1), "Number");
assertEquals(getClass(""), "String");
assertEquals(getClass(new (function MyClass(){})()), "MyClass");
assertEquals(getClass(document.createElement('div')), "HTMLDivElement");
assertEquals(getClass(document.createElement('span')), "HTMLSpanElement");