Custom Sidekick Dialog in CQ5

Set up your file structure something like this:

/apps/your-site/components/page
  -> yourPage
      -> clientlibs
          -> js
              -> customSidekickDialog.js
          -> .content.xml
          -> js.txt
      -> customDialog.xml
      -> ...

customSidekickDialog.js

;(function(CQ){
  
	var DIALOG_PATH = '/apps/your-project/path/to/customDialog.xml';
	var DIALOG_PROPS = '/jcr:content/were/dialog/properties/should/be/stored';

	// add dialog to default actions
	CQ.wcm.Sidekick.DEFAULT_ACTIONS.push({
		
		context: CQ.wcm.Sidekick.PAGE,
		text: 'Title of your dialog in sidekick',
		handler: function() {
			// set up dialog configuration
			var dialogConfig = CQ.WCM.getDialogConfig(DIALOG_PATH);
			dialogConfig.success = function(form, action){
				// reload page on dialog success
				CQ.Util.reload(CQ.WCM.getContentWindow());
			};
			dialogConfig.failure = function(form, action){
				// alert user when dialog fails
				var resp = CQ.HTTP.buildPostResponseFromHTML(action.response);
				CQ.Ext.Msg.alert(response.headers[CQ.HTTP.HEADER_MESSAGE]);
			};
			
			// prepare and show dialog
			var dialog = CQ.WCM.getDialog(dialogConfig, DIALOG_PATH);
			dialog.loadContent(this.getPath() + DIALOG_PROPS);
			dialog.setTitle('Title of your dialog in dialog window');
			dialog.show();
		}

	});
	
})(CQ);

launchSidekick.js

// replace sidekick launch in init.jsp with this
CQ.WCM.launchSidekick("<%= currentPage.getPath() %>", {
    propsDialog: "<%= dlgPath == null ? "" : dlgPath %>",
    locked: <%= currentPage.isLocked() %>,
    previewReload: "true",
    actions: CQ.wcm.Sidekick.DEFAULT_ACTIONS // make sure actions is explicitly specified
});