<form action="" target="frame" id="form">
<iframe name="frame" src="https://docs.google.com/forms/d/e/1FAIpQLSdIM6PXOc0VRW7kycFs_2RkJIlM6V4woLqrE3A94Izctpl4cw/viewform" frameborder="0" height="100%" width="100%" id="iframe"></iframe>
</form>
if( document.getElementById('form') ){
// как проверит if
}