Working with HTML classes like jQuery's addClass and removeClass

classes.js

function isElement(obj) {
  try {
    // For Firefox, Opera and Chrome
    return obj instanceof HTMLElement;
  }
  catch(e){
    // IE Bugfix
    return (typeof obj==="object") &&
      (obj.nodeType===1) && (typeof obj.style === "object") &&
      (typeof obj.ownerDocument ==="object");
  }
}

// Get classes from a DOM Element
function getClasses(elem) {
  if(isElement(elem)) {
    return elem.className.split(/\s+/)
  }
  return null;
}

// Check the classes of a DOM Element
function hasClass(elem, clazz) {
  if(isElement(elem)) {
    var _classes = getClasses(elem);
    for(var i = 0; i < _classes.length; i++) {
      if(_classes[i] == clazz) return true
    }
    return false
  }
  return null;
}

var myElement = document.getElementById('myElement'); // #myElement.testClass
var myClasses = getClasses(myElement);                // [testClass]
if(hasClass(myElement, "testClass") {                 // true
  alert("My element has the class 'testClass'!");
}