In Jenkins, you can export arbitrary server-side Java object to JavaScript via a proxy, then invoke their methods from JavaScript. In this sample, we call a method on the server to increment a counter. This object is a singleton, so you'll see the same counter value across all the browsers.

To expose a method of a Java class to JavaScript proxy, annotate the method with @JavaScriptMethod. For security reasons, only public methods on public classes annotated with this annotation are invokable from browsers:

Then from Jelly scripts, use st:bind tag to export a Java object into a proxy. The "value" attribute evaluates to a server-side Java object to be exported, and the tag produces a JavaScript expression that creates a proxy. In the example below, we are pretending that the JEXL expression evaluates to some instance of Foo.

Below, you can find the sample for the adjunct to include. More information about adjuncts can be found on the security page.

Invoking method

As you can see above, one can invoke methods on the proxy created by the st:bind tag. The JavaScript method takes the arguments that the Java method takes, then it can optionally take a function as an additional parameter, which is used as a callback method when the return value is available. The callback method receives an Ajax.Response object.

If the Java method returns an object value (such as int, String, Collection, Object[], JSONObject, etc.), you can use the responseObject() method to evaluate the response into a JavaScript object and use it. If the Java method renders more complex HTTP response (for example by writing directly to StaplerResponse or returning an HttpResponse), JavaScript can use other Ajax.Response methods to access the full HTTP response.

The method call uses XmlHttpRequest underneath, and it gets eventually routed to the corresponding method call on the exact instance that was exported.

Tips

Parameters of the server Java method.

The Java method can define arbitrary number of parameters for JavaScript. Each parameter is converted from JSON to Java via StaplerRequest.bindJSON, so aside from primitive Java data types and typeless JSONObject / JSONArray, you can use Stapler databinding to accept typed structured data.

After defining the parameters from JavaScript, you can additionally define parameters that are injectable by Stapler, such as StaplerRequest or StaplerResponse.

Exporting null

If the value attribute of a st:bind tag evaluates to null, then the corresponding JavaScript proxy will be null.