Automatically fill a form field with text from another field using checkbox :: JS/Wordpress/Contact Form 7

gistfile1.txt

/* Header: */
<script type="text/javascript">
		function FillBilling(f) {
  if(f.billingtoo.checked == true) {
    f.invoice_textarea.value = f.deliveryaddress.value;
  }
}
		</script>
		
	/* in the form - using Contact Form 7 */
	
	<p>Delivery Address <span style="color: #ff0000">*</span></p>
[textarea* textarea-572 id:deliveryaddress class:input-text]

<input type="checkbox" name="billingtoo" onclick="FillBilling(this.form)">
<em>Check this box if Invoice Address and Delivery Address are the same.</em><br>

<p>Invoice Address <span style="color: #ff0000">*</span></p>
[textarea* textarea-252 id:invoice_textarea class:input-text]
<br>