function HideContent(d) 
{
	if (d.length < 1) { return; }
	document.getElementById(d).style.display = "none";
}

function ShowContent(d) 
{
	if (d.length < 1) { return; }
	document.getElementById(d).style.display = "";
}

function ReverseContentDisplay(d) 
{
	if (d.length < 1) { return; }
	if (document.getElementById(d).style.display == "none") 
		{ document.getElementById(d).style.display = ""; }
	else { document.getElementById(d).style.display = "none"; }
}

function showAbout()
{
	ReverseContentDisplay('about'); 
	HideContent('contact'); 
}
function showContact()
{
	HideContent('about'); 
	ReverseContentDisplay('contact'); 
}

function isEmpty(name, email, subject, message)
{
	//change "field1, field2 and field3" to your field names
	strfield1 = document.forms[0].name.value;
	strfield3 = document.forms[0].subject.value;
	strfield4 = document.forms[0].message.value;

	//name field
	if (strfield1 == "" || strfield1 == null || !isNaN(strfield1) || strfield1.charAt(0) == ' ')
	{
		alert("Please enter your name.");
		return false;
	}

	//subject field 
	if (strfield3 == "" || strfield3 == null || strfield3.charAt(0) == ' ')
	{
		alert("Please enter a subject.")
		return false;
	}

	//message field 
	if (strfield4 == "" || strfield4 == null || strfield4.charAt(0) == ' ')
	{
		alert("Please enter a message.")
		return false;
	}
	return true;
}

//function to check valid email address
function isValidEmail(strEmail)
{
  validRegExp = /^[^@]+@[^@]+.[a-z]{2,}$/i;

  strEmail = document.forms[0].email.value;

  // search email text for regular exp matches
  if (strEmail.search(validRegExp) == -1) 
  {
		alert("Please enter a valid email.");
		return false;
	} 
	return true; 
}

function checkForm(form)
{
	if (isEmpty(form.field1))
	{
  	if (isEmpty(form.field3))
  	{
    	if (isEmpty(form.field4))
    	{
				if (isValidEmail(form.email))
				{
		  		return true;
				}
	  	}
  	}
	}
	return false;
}