Salesforce - How to call an apex class with java script

visualforce page Java script

 // read the parameter values and get the values   
  var jobId ='{!$CurrentPage.parameters.jobId}';  
  // pass the values and retrive the URL  
  var urls = sforce.apex.execute("globalClass","getURL",{jobId:jobId});  
  document.getElementById("banner").src = urls;  

webservice method

/**  
  *  Author: Hasantha Liyanage  
  * Created: 2014-12-10  
  * Summary: This is to get the URL according to the id and which reads a custom setting to retrive some values  
  **/  
 global class JobOrderControllerExtension {  
   webservice static String getLisenseeURL(String strJobId) {  
     if (String.isEmpty(strJobId)) { return ''; }  
     // capture first 15 chars of id only  
     // ensure only valid id characters  
     if(validateId(strJobId)){ return ''; }  
     Account acct = [  
       SELECT  
         Name  
       FROM Account  
       WHERE(Id = : strJobId)  
       LIMIT 1  
     ];  
     // get the url from custom setting mapped with account name  
     return getUrl(acct.Name);  
   }  
     /**  
      *  get the url by reading the custom setting  
      *   parameter: licensee name retrived from account  
      **/  
   private static String getUrl(String name) {  
     Map < String, Banners__c > mapBanners =Banners__c.getAll();  
     for (Banners__c banner: mapBanners.values()) {  
       if (!String.isEmpty(banner.Name) && !String.isEmpty(name) && banner.Name.equals(name)) {  
         return banner.URL__c;  
       }  
     }  
     return null;  
   }  
   static public boolean validateId(String Idparam) {  
       String id = String.escapeSingleQuotes(Idparam);  
       if(Pattern.matches('[a-zA-Z0-9]{15}', id)) {  
         return true;  
       }  
       return false;  
   }  
 }