var knop = document.getElementById("verzend_knop");
var naam = document.getElementById("naam");
var email = document.getElementById("email");
var bericht = document.getElementById("bericht");

function checkInput(){
	if (naam.value !== ""
	&& email.value.search(/^([0-9a-zA-Z]+[-._+&])*[0-9a-zA-Z]+@([-0-9a-zA-Z]+[.])+[a-zA-Z]{2,6}$/) == 0
	&& bericht.value !== "")
	{
		knop.disabled=false;
		knop.value = "Verzend";
	}
	else
	{
		knop.disabled=true;
		knop.value = "Verzend (Vul alle velden correct in)";
	}
}

naam.onkeyup = checkInput;
email.onkeyup = checkInput;
bericht.onkeyup = checkInput;
naam.onchange = checkInput;
email.onchange = checkInput;
bericht.onchange = checkInput;
knop.disabled=true;

checkInput();

initialize();