<!DOCTYPE html> <html> <body> <form name="theForm"> <select name="theSelect" style="width: auto"> <option>xxxxxxxxxx</option> </select> </form> <script> // Flush reflow document.body.offsetWidth; document.theForm.theSelect.style.width='30em'; document.body.offsetWidth; document.theForm.theSelect.style.width='auto'; </script> </body> </html>