var FormHelper = function () {
};
 
//now create an instance of the object.
var fh1 = new FormHelper();

var FormHelper = function (pid) {
  this.id = pid;
};
 
var fh1 = new FormHelper("test-form");
 
alert(fh1.id);

var FormHelper = function (pid) {
  var id = pid;
};
 
var fh1 = new FormHelper("test-form");
 
alert(fh1.id);

var FormHelper = function (pid) {
 
  var id = pid;
 
  this.getFormId = function () {
    return id;
  };
 
};
 
var fh1 = new FormHelper("test-form");
 
alert(fh1.getFormId());

var FormHelper = function (pid) {
 
  var that = this;
  this.id = pid;  
 
  var getFormEl = function () {
    var id = that.id;
    return document.getElementById(id);
  };
 
  this.getForm = function () {
    return getFormEl();
  };
 
};
 
var fh1 = new FormHelper("test-form");
 
alert(fh1.getForm());

/**
 * My own namespace so I'm not polluting the global namespace.
 */
CWS = {};
 
/**
 * An object constructor to demonstrate public, private and privileged
 * object members.
 */
CWS.FormHelper = function (id) {
 
  /**
   * We use the "that" variable in private functions where the "this"
   * variable is not what you might expect. The "that" and "formEl"
   * variables are private object members.
   */
  var that = this;
  var formEl = false;
 
  /**
   * This is a public object member. Note the use of the "this" variable.
   * That's what makes an object member public.
   */
  this.formId = id;
 
  /**
   * Set some initial values.
   *
   * A private object member.
   */
  var init = function () {
 
    /**
     * The "this" variable in the context of private object members
     * is the window object which is not what we want. The below
     * statement results in id being assigned with undefined since formId
     * was assigned to the FormHelper instance and not the window object.
     */
    var id = this.formId;
 
    /**
     * Luckily we were smart and created the "that" variable which is a
     * a reference to the FormHelper instance.
     */
    id = that.formId;
 
    if (YAHOO.lang.isString(id))
    {
      /**
       * This assigns the form element to the private variable formEl.
       */
      formEl = document.getElementById(id);
    }
 
    if (YAHOO.lang.isObject(formEl))
    {
      return true;
    }
    else
    {
      return false
    }
  }
 
  /**
   * Gets a form field element from a form.
   *
   * This is a private function.
   */
  var getField = function (name) {
 
    /**
     * Note that "formEl", a private object member is accessed from this
     * private function without the "this" variable.
     */
    for (var i = 0; i < formEl.elements.length; i++)
    {
      var el = formEl.elements[i];
 
      if (el.name == name)
      {
        return el;
      }
    }
 
    return false;
  };
 
  /**
   * Gets the current value from a form field.
   *
   * This is a public function, and public functions can access private
   * object members.
   */
  this.getValue = function (name) {
 
    /**
     * Here we're calling a private function. Note that getField is not
     * prefixed by "this" or "that".
     */
    var el = getField(name);
 
    if (!el)
    {
      return false;
    }
 
    return el.value;
  };
 
  /**
   * This is not a great practice but gives us the opportunity to use the
   * "that" variable.
   */
  if (!init())
  {
    alert ("Failed to create a CWS.FormHelper instance.");
  }
};
 
var fh1 = new CWS.FormHelper ("test-form");
 
/**
 * Calling the below results in an error since the function is private.
 */
try
{
  var el = fh1.getField("test-form"); //error
}
catch (e)
{
  //alert("We tried to call a private object member!");
}
 
/**
 * The below assigns undefined to the global variable "formEl" it's trying
 * to access a private object member.
 */
var formEl = fh1.formEl;
 
if (!YAHOO.lang.isUndefined(formEl))
{
  alert ("This alert never happens.");
}
 
/**
 * We must use the privileged getValue function to get the data we want. Public
 * functions are privileged.
 */
var inputValue = fh1.getValue ("test-input");