To get the id of a form with a drop-down list, use the id property in JavaScript.
Example
You can try to run the following code to find the id of a form containing drop-down list −
<!DOCTYPE html> <html> <body> <form id="myForm1"> <button id="btn" type="button" value="my_button">Demo</button> </form><br> <form id="myForm2"> <select id="mySelect"> <option>One</option> <option>Two</option> <option>Three</option> </select> </form> <script> var val = document.getElementById("mySelect").form.id; document.write("<br>Form id with dropdown: "+val); </script> </body> </html>