function validate_form(){ 
 
   var senderName = document.contactform.sender_name.value;
   var senderAdress = document.contactform.sender_adress.value;
   var senderEmail = document.contactform.sender_email.value;
   var senderTel = document.contactform.sender_tel.value;
   var subject = document.contactform.subject.value; 
   var message = document.contactform.message.value; 
   var invalidChar = " /:,;"; 
   var atPos = document.contactform.sender_email.value.indexOf("@",1); 
   var periodPos = document.contactform.sender_email.value.indexOf(".",atPos); 
    
   if(senderName == ""){ //namnet ska vara ifyllt
      alert("Contact person is missing") 
      document.contactform.sender_name.focus() 
      return false; 
   }
   
    if(senderAdress == ""){ //namnet ska vara ifyllt
      alert("Your adress is missing") 
      document.contactform.sender_adress.focus() 
      return false; 
   }
       
   if(senderEmail == ""){ // mailen måste vara ifylld.
      alert("Your email is missing") 
      document.contactform.sender_email.focus() 
      return false; 
   }
   
    if(senderTel == ""){ // mailen måste vara ifylld.
      alert("Your Tel. is missing") 
      document.contactform.sender_tel.focus() 
      return false; 
   }

    if(subject == ""){ // mailen måste vara ifylld.
      alert("Subject is missing") 
      document.contactform.subject.focus() 
      return false; 
   }
    
   for(i=0; i<invalidChar.length; i++){ // Checking for invalid characters in email 
      badChar = invalidChar.charAt(i); 
      if(senderEmail.indexOf(badChar,0) > -1){ 
         alert("Not valid email"); 
         document.contactform.sender_email.focus() 
         document.contactform.sender_email.select() 
         return false; 
      } 
       
   } 
    
   if(atPos == -1){ // @ is missing
      alert("Not valid email"); 
      document.contactform.sender_email.focus() 
      document.contactform.sender_email.select() 
      return false; 
   } 
    
   if(senderEmail.indexOf("@",atPos+1) != -1){ // En e-postadress kan endast innehålla Ett @ 
      alert("Not valid email"); 
      document.contactform.sender_email.focus() 
      document.contactform.sender_email.select() 
      return false; 
   } 
    
   if(periodPos == -1){ // måste "." vara en punkt efter @ 
      alert("Not valid email"); 
      document.contactform.sender_email.focus() 
      document.contactform.sender_email.select() 
      return false; 
   } 
 
   if(periodPos+3 > senderEmail.length){ // två bokstäver efter punkten i mailadressen 
      alert("Not valid email"); 
      document.contactform.sender_email.focus() 
      document.contactform.sender_email.select() 
      return false; 
   } 
       
   
       
   if(message == ""){ //validering för meddelandet
      alert("Please write a message") 
      document.contactform.message.focus() 
      return false; 
   } 
       
   return true; 
}