Selectbox error

[ByteCoder]

I have a selectbox and the user can choose languages through onChange ();

Now, this does not work. I get a JavaScript error, but do not know why.

 <form class="languageSwitch" name="form1" action=""> 
              <select class="taalKeuze" name="select1" onchange="languageChange();"> 
                  <option value="NL" selected="selected"> Dutch - EN </ option> 
                  <option value="UK"> English - UK </ option> 
                  <option value="DE"> Deutsch - DE </ option> 
              </ select> 
          </ form>

JavaScript

<script type="text/javascript"> 
      Change language function () ( 
        
          if (document.form1.select1.value == NL) 
              window.location = 'default.php'; 
            
          else if (document.form1.select1.value == UK) 
              window.location = 'default uk.php'; 
                
          else if (document.form1.select1.value == DE) 
              window.location = 'default de.php'; 
        
      ) 
  </ script>

The error: 'EN' is not defined
Anyone for help ??

[ByteCoder]

Edit / So when I EN and DE, etc. in a varriabele continued, it was error away but it still does not work. When I use the letters in the value changed the numbers. 1, 2, 3 everything was suddenly so. Why does it happens with numbers and letters ?

It is already solved

[kelfro]

Because the text in quotation marks should post. Now the variables.

if (document.form1.select1.value == NL)

must therefore be

 if (document.form1.select1.value == 'EN')

A number (integer) may be used without quotation marks.