unable to execute URLEncodedFormat when using window.location.href in a javascript

i have an html form in a cfm file and i want to get the value of a textarea before the form is submited, so i use a javascript to get this value and to reload the file the passed through the URL. the textarea may have special characters so i must use URLEncodedFormat, the problem is that when i use this it returns the name of the variable not the value. see the code bellow:

<script>
function check_answer()
{
var answer_text=document.form1.textarea1.value;
<CFOUTPUT>
window.location.href="test.cfm?answer_text=#URLEncodedFormat("+answer_text+")#";
</CFOUTPUT>
}
</script>

when i print the answer_text in test.cfm i get +answer_text+

i don't have any problem to use another method in order to get the value of the textarea

any help is welcome ioanna