Someone

Object.prototype.inherit = function(superObj, overWriteMember) {
  /*
    inherit all members and objects of object 'superObj'
    
    if 'this' object already has the data member, overWriteMember
    will decide whether or not to overwrite the member
  */
  
  var m;
  
  for (m in superObj) {
    if (this[m] == undefined || overWriteMember)
      this[m] = superObj[m];
  }
}


// example

  this.inherit( ( new TabClass( document.getElementById("iframe_content") , document.createElement("DIV") ) ) );