Webix Jet uses es6, so it will not work without transpiler
If you are interested only in modern browsers with native es6 support, it possible to run the code without the bundler, similar to the way how jet snippets work ( https://snippet.webix.com/jetmenu ), still it means placing all functionality in a single js file which will result in a mess for any non-trivial app.
If you need to implement very simple functionality, it has sense to init webix components directly, instead of using Webix Jet.