Execute Background Script from Client Script: Retrieve SysID

bgScriptFromClient.js

var sysId = 'someSysId';
var gck = typeof g_ck != 'undefined' ? g_ck : 'insertOptionalTokenHere'; //if AppNavigator is shown, it is retrieved automatically
jQuery.ajax({
		url:  'sys.scripts.do',
		method: 'GET', //POST does not work somehow
		headers: {
			'X-UserToken': gck,
			'Cache-Control': 'no-cache',
			'Accept': 'application/json',
			'Content-Type': 'application/json'
		},
        data: {
            script: 'function findSysID(e){var s,d,n=new GlideRecord("sys_db_object");n.addEncodedQuery("super_class=NULL^nameNOT LIKEts_^nameNOT LIKEsysx_^nameNOT LIKEv_^sys_update_nameISNOTEMPTY^nameNOT LIKE00"),n.query();for(var a=[];n.next();)d=n.name+"",(s=new GlideRecord(d)).isValid()&&(s.addQuery("sys_id",e),s.queryNoDomain(),s.setLimit(1),s.query(),s.hasNext()&&a.push(d));gs.print("###"+a+"###")}findSysID("'+sysId+'");',
            runscript: "Run script",
            sysparm_ck: gck,
            sys_scope: 'e24e9692d7702100738dc0da9e6103dd'
        }
	}).done(function (rspns) {
		answer = rspns.match(/###(.*)###/);
		console.log(answer != null ? answer[1] : rspns);
	}).fail(function (jqXHR, textStatus) {
		console.error(textStatus);
	});