Redirection

Could someone please clue me in to why this may not be working?

<form onsubmit="validateSearchForm(this.searchTerm);" style="margin: 0; "name="form1" method="post" action=""> <input style="margin-bottom: 3px;" name="searchTerm" type="text" size="23"> <input name="Search" type="submit" class="button" value="Search"> </form> <script language="JavaScript" type="text/javascript"> function validateSearchForm(field) { if(field.value.length == 0) { alert('Please enter a search term.'); return; } else { this.location.href='searchresults.php?search_term=' + field.value; } } </script>

The test works but when the field lengh is greater than 0 the redirect does not work.

Thanks very much.