Ok, i found the error.
It seems that Webix Jet in using RequireJS for “connecting” JS modules.
A very useful article for those that want to understand the basic code behind Jet is here:
http://www.nicolasbottarini.com/using-requirejs-for-symfony-2-development/
Im my case i found out that you in “index.html” when including require.js you also have to define the path to the first JS of Webix Jet.
So here:
{{script type=“text/javascript” data-main=“app” src=“libs/require.js”}}{{/script}}
…the data-main=“app” …the “app” should be the path to the app.js without extension. If this app.js is not in the root(like with the framework like Symfony), then you have to define its path here…like data-main="/somefolder/otherfolder/app".