Can not add shortcode button with name "slider"

@jose Castaneda

Yes. I disabled all plugins and tried with Twenty Fourteen. Here is code in functions.php

function wpi_post_editor_buttonhooks() {
	// Only add hooks when the current user has permissions AND is in Rich Text editor mode
	if ( ( current_user_can('edit_posts') || current_user_can('edit_pages') ) && get_user_option('rich_editing') ) {
		add_filter("mce_external_plugins", "wpi_post_editor_register_tinymce_javascript");
		add_filter('mce_buttons', 'wpi_post_editor_register_buttons');
	}
}

function wpi_post_editor_register_buttons($buttons) {
   array_push($buttons, '|', 'slider');
   return $buttons;
}

// Load the TinyMCE plugin : editor_plugin.js (wp2.5)
function wpi_post_editor_register_tinymce_javascript($plugin_array) {
   $plugin_array['wpi_post_editor'] = get_template_directory_uri() . '/js/editor.js';
   return $plugin_array;
}

// init process for button control
add_action('init', 'wpi_post_editor_buttonhooks');

And here is the code of editor.js:

jQuery(function($) {
	(function() {
		// prepare box for input content
		tinymce.create('tinymce.plugins.Wpi_post_editor', {
			init : function(ed, url) {
				// Contact
				ed.addButton('slider', {
					title : 'Slider',
					cmd : 'slider',
					image : 'slider.png'
				});
			},
		});
		// Register plugin
		tinymce.PluginManager.add( 'wpi_post_editor', tinymce.plugins.Wpi_post_editor );
	})();
});