Question

I made a subclass of goog.ui.Button in my Google Closure javascript.

/**
 * @fileoverview This button makes a new widget.
 * @author David Faux
 */

goog.provide('app.ui.NewWidgetButton');

goog.require('goog.ui.Button');



/**
 * Button for creating a new widget.
 * @constructor
 * @param {goog.ui.ButtonRenderer=} opt_renderer Optional renderer used to
 *    render or decorate the button.
 * @param {goog.dom.DomHelper=} opt_domHelper Optional DOM hepler, used for
 *    document interaction.
 * @extends {goog.ui.Button}
 */
app.ui.NewWidgetButton = function(opt_renderer, opt_domHelper) {
  goog.base(
    this,
    /** @type {goog.ui.ControlContent} */ 'New Widget',
    opt_renderer,
    opt_domHelper);
}
goog.inherits(app.ui.NewWidgetButton, goog.ui.Button);

However, when I instantiate this button with var newButton = app.ui.NewWidgetButton();, I get an error in Chrome Console:

`Uncaught TypeError: Object #<Object> has no method 'setContentInternal'`

I looked up the method setContentInternal, and it seemed to be a method of the class goog.ui.Control, which is a superclass of goog.ui.Button, so I am befuddled as to why this method is undefined.

Answer 1

The instantiation of newButton is missing the new keyword. Adding the new keyword fixes the error.

var newButton = new app.ui.NewWidgetButton();

Set the Closure Compiler flag --warning_level=VERBOSE to generate an error such as the following:

WARNING – Constructor function (new:app.ui.NewWidgetButton, (goog.ui.ButtonRenderer|null)=, (goog.dom.DomHelper|null)=): undefined should be called with the “new” keyword