... 
var plz59602= "4" 
var plz59889= "3" 
var plz59909= "2" 
var plz59939= "2" 
 
   var feld = ""; 
     
   this.resetForm("plz_zone"); 
 
   var plz = this.getField("t_PLZ").value; 
   var plz_hilf = plz + "*"; 
       
   if(plz_hilf.length == 5) 
   { 
      var plz_hilf = "0" + plz_hilf; 
   } 
        
   plz_hilf = plz_hilf.substr(0,5); 
   var zone = this.getField("plz_zone").value; 
 
   feld = "plz" + plz_hilf; 
   this.getField("plz_zone").value = eval(feld);