vaadin-framework/documentation/articles/UsingAJavaScriptLibraryOrAStyleSheetInAnAddOn.asciidoc

---
title: Using A JavaScript Library Or A Style Sheet In An Add On
order: 40
layout: page
---

[[using-a-javascript-library-or-a-style-sheet-in-an-addon]]
Using a JavaScript library or a style sheet in an add-on
--------------------------------------------------------

Including style sheets or JavaScript files in your add-ons or as a part
of your application can now be done by adding a `@StyleSheet` or
`@JavaScript` annotation to a `Component` or `Extension` class. Each
annotation takes a list of strings with URLs to the resources that
should be loaded on the page before the framework initializes the
client-side `Component` or `Extension`.

The URLs can either be complete absolute urls (e.g. https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js) or
relative URLs (e.g. _redbutton.css_). A relative URL is converted to a
special URL that will download the file from the Java package where the
defining class is located. This means that e.g.
`@StyleSheet({"redbutton.css"})` on the class `com.example.RedButton` will
cause the file `com/example/redbutton.css` on the classpath to be loaded
in the browser. `@JavaScript` works in exactly the same way - see
<<IntegratingAJavaScriptComponent#integrating-a-javascript-component,
Integrating a JavaScript component>> for a practical example.

[source,java]
....
@StyleSheet("redbutton.css")
public class RedButton extends NativeButton {
  public RedButton(String caption) {
    super(caption);
    addStyleName("redButton");
  }
}
....

In this simple example, the `RedButton` component just adds a `redButton`
style name to a normal `NativeButton`. _redbutton.css_ is located in the
same folder as _RedButton.java_ and has this content:

[source,css]
....
.redButton {
  background-color: red;
}
....

This new mechanism makes it very easy to include style sheet or
JavaScript files with add-ons and automatically load them in the browser
when the add-on is used.

[WARNING]
.Security Warning
====
Do note that third-party JavaScript code can be dangerous 
(https://www.owasp.org/index.php/3rd_Party_Javascript_Management_Cheat_Sheet), 
and you should take into account the security risks of using such. 

====