Active Choices Reactive Parameter for parametrizing JavaScript from a Jenkins Global Variable

AC_IMAGE_GALLERY.groovy

import jenkins.*
import jenkins.model.*
import hudson.*
import hudson.model.*
import org.kohsuke.stapler.Stapler
import groovy.text.SimpleTemplateEngine

def sessionID= Stapler.getCurrentRequest().getSession().getId() 
instance = Jenkins.getInstance()
globalNodeProperties = instance.getGlobalNodeProperties()
envVarsNodePropertyList = globalNodeProperties.getAll(hudson.slaves.EnvironmentVariablesNodeProperty.class)
envVars = envVarsNodePropertyList.get(0).getEnvVars()
osdJs= envVars['OPENSEADRAGON_JS']
env=System.getenv()

helperJavaScriptTemplatePath="${env['JENKINS_HOME']}/jobs/${jenkinsProject.name}/buildScripts/imageGallery.jst"
helperJavaScriptTemplate= new File(helperJavaScriptTemplatePath as String)
def simple = new SimpleTemplateEngine()
def source = helperJavaScriptTemplate.text
def binding = [osdJs: osdJs]
def helperJavaScript= simple.createTemplate(source).make(binding).toString()

/*
we also write a copy of the parametrized helper JS
it is re-used in the build report
*/
customHelperJs='imageGallery.js'
new File("${envVars['SESSIONS_WORKSPACE']}/ASSAY_EXPLORER_$sessionID").mkdir()
output=new File("${envVars['SESSIONS_WORKSPACE']}/ASSAY_EXPLORER_$sessionID/$customHelperJs")

fileWriter=output.newWriter(false)
fileWriter<<helperJavaScript
fileWriter.flush()
fileWriter.close()

imageGalleryHtml= """<script type="text/javascript"> ${helperJavaScript} </script>"""


html="""
<input id="fillStrategy" name="value" type="text" class="setting-input   " value="" hidden=true>
<div id="openseadragon1" style="width: 1200px; height: 720px;"></div>

<script src="/userContent/js/$osdJs/openseadragon.min.js"></script>
<script src="/userContent/js/openseadragon-filtering.js"></script>
<script src="/userContent/js/caman.full.min.js"></script>
"""
return html+imageGalleryHtml