PrimeFaces.current() is a helper with various utilities.
<style>
    .ui-log {
        left: 600px;
        top: 100px;
    }
</style>
<script>
    function handleComplete(xhr, status, args) {
        if (args.validationFailed) {
            PrimeFaces.debug("Validation Failed");
        } else {
            PrimeFaces.debug("Save:" + args.saved);
            PrimeFaces.debug("FirstName: " + args.user.firstname + ", Lastname: " + args.user.lastname);
        }
    }
</script>
<div class="card">
    <h:form id="form">
        <p:messages>
           <p:autoUpdate />
        </p:messages>
        <h:panelGrid columns="2" cellpadding="7" id="panel">
            <p:outputLabel for="firstname" value="Firstname:"/>
            <p:inputText id="firstname" value="#{requestContextView.user.firstname}" required="true"/>
            <p:outputLabel for="surname" value="Lastname:"/>
            <p:inputText id="surname" value="#{requestContextView.user.lastname}" required="true"/>
        </h:panelGrid>
        <p:commandButton value="Save" action="#{requestContextView.save}" styleClass="mt-2"
                         oncomplete="handleComplete(xhr, status, args)"/>
        <p:log/>
    </h:form>
</div>
package org.primefaces.showcase.view.misc;
import jakarta.annotation.PostConstruct;
import jakarta.enterprise.context.RequestScoped;
import jakarta.faces.application.FacesMessage;
import jakarta.faces.context.FacesContext;
import jakarta.inject.Named;
import io.quarkus.runtime.annotations.RegisterForReflection;
import org.primefaces.PrimeFaces;
import org.primefaces.showcase.domain.User;
@Named
@RequestScoped
@RegisterForReflection(serialization = true)
public class RequestContextView {
    private User user;
    @PostConstruct
    public void init() {
        user = new User();
        if (!FacesContext.getCurrentInstance().isPostback()) {
            PrimeFaces.current().executeScript("PrimeFaces.info('This message is added from backing bean.')");
        }
    }
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }
    public void save() {
        PrimeFaces.current().ajax().addCallbackParam("saved", true);    //basic parameter
        PrimeFaces.current().ajax().addCallbackParam("user", user);     //pojo as json
        //execute javascript oncomplete
        PrimeFaces.current().executeScript("PrimeFaces.info('Hello from the Backing Bean');");
        //update panel
        PrimeFaces.current().ajax().update("form:panel");
        //scroll to panel
        PrimeFaces.current().scrollTo("form:panel");
        //add facesmessage
        FacesContext.getCurrentInstance().addMessage(null, new FacesMessage("Success", "Success"));
    }
}