Passing extra parameter to f:ajax onevent function
Wrap it in an anonymous function wherein you pass it as extra argument.
<h:commandLink value="do something boy!"> <f:ajax render="@form" execute="@form" listener="#{myBean.doStuff}" onevent="function(data) { showProgress(data, 'extraValue') }" /></h:commandLink>with
function showProgress(data, extraParam) { // Use "data" argument the usual way. // The "extraParam" argument will contain "extraValue" in above example.}