example.html

<!-- in the head of main.gsp -->

<script>
(function () {
      var json = <%= (json ?: []) as JSON  %>;
      MyApp.config = json;
})();
</script>

JsonFilters.groovy

import org.codehaus.groovy.grails.commons.ConfigurationHolder
import org.codehaus.groovy.grails.web.servlet.mvc.GrailsWebRequest
import grails.util.Environment
import org.grails.plugins.settings.Setting

class JsonFilters {

    def securityService
    
    def filters = {
        all(controller: '*', action: '*') {
            after = { model ->
                if (!request.xhr) {
                    model = model ?: [:]
                    Map existingJson = model.json ?: [:]
                    model.json = [
                            serverURL: ConfigurationHolder.config?.grails?.serverURL,
                            contextPath: GrailsWebRequest.lookup(request).contextPath,
                            env: Environment.current.name,
                            someUrl: grailsApplication.config.someservice.jsonsuggest.url,
                            userLogin: securityService.userLogin?.mapify(),
                            params: params
                    ] + existingJson
                }
            }
        }
    }
}