utils/dom.js
function createDom(tagName, opt_className) {
  var element = document.createElement(tagName);
  if (opt_className) {
    element.className = opt_className;
  }
  return element;
}
function createDom(tagName, opt_className) {
  var element = document.createElement(tagName);
  if (opt_className) {
    element.className = opt_className;
  }
  return element;
}
function createDom ( tagName , opt_className ) { var element = document . createElement ( tagName ) ; if ( opt_className ) { element . className = opt_className ; } return element ; }
Creates a dom element and optionally adds a class name.
@param {string} tagName Element's tag name.
@param {string?} opt_className Class name to add.
@return {Element} Created element.
Creates a dom element and optionally adds a class name .