Scripts.html

<script>
(function(e,t,n){
  var r=e.querySelectorAll("html")[0];
  r.className=r.className.replace(/(^|\s)no-js(\s|$)/,"$1js$2")})(document,window,0);

/*
	By Osvaldas Valutis, www.osvaldas.info
	Available for use under the MIT License
*/

//this script was modified for that particular form demonstration

'use strict';



;( function ( document, window, index )
{
	var inputs = document.querySelectorAll( '.upload input' );
    
	Array.prototype.forEach.call( inputs, function( input )
	{
		var label	 = input.nextElementSibling.nextElementSibling,
			labelVal = label.innerHTML;

		input.addEventListener( 'change', function( e )
		{
			var fileName = e.target.value.split( '\\' ).pop();

			if( fileName )
				label.innerHTML = fileName;
			else
				label.innerHTML = labelVal;
                
		});

		// Firefox bug fix
		input.addEventListener( 'focus', function(){ input.classList.add( 'has-focus' ); });
		input.addEventListener( 'blur', function(){ input.classList.remove( 'has-focus' ); });
	});
}( document, window, 0 ));


function preventSubmit() {
  var frm = document.getElementById('upload_form');
  
  frm.addEventListener('submit', function(event) {
            event.preventDefault();
          }, false);
}
window.addEventListener('load', preventSubmit);

function formSubmit(formObject) {
  document.getElementsByClassName("required-asterisk")[0].style.display = "none";
  document.getElementsByClassName("form-content")[0].innerHTML = 'Sending...';
  google.script.run.withSuccessHandler(onSuccess).withFailureHandler(onFailure).uploadFiles(formObject);
}

function onSuccess(respond) {
  document.getElementsByClassName("form-content")[0].innerHTML = respond;
}

function onFailure(respond) {
  document.getElementsByClassName("form-content")[0].innerHTML = respond;
}

</script>