I have this pice of code:

    function validator() {
    var l1 = document.calculation.l1.value;
    var l2 = document.calculation.l2.value;
    var right = document.calculation.right.value;
     
 
if (l1 == null || l1 == "") alert("error ");
else if (l1 == null || l2 == "") alert("error");
else if (l1 == null || right == "") alert("error");
else if (right == 1) { alert("Correct"); }
 
  else { alert("Incorrect incorect"); } 
 
return false;
};

In Firefox is ok, but in Chrome the alert box is displayed before pressing the Submit button from my form. What can be wrong here?

Where did you put validator() ? On which event?

Well, validator is the function that I have for a small form.
I'm calling it this way (the function is in a speratate file that I have declared it in header):

...............
...............
<input type="text" value=""  name="l2" size="10" />

<input type="submit" value="Check your answer" onClick="return validator();">  


  
<script type="text/javascript"><!--//--><![CDATA[//><!--
onClick(validator());  //--><!]]&gt;</script>

Try to change it to onSubmit and put that tag inside the <form> element like in this example:
http://www.w3schools.com/jsref/event_form_onsubmit.asp

So what is the script element in that code supposed to be doing?