function checkName(veld,melding,minimumlength)
{
 veldnaam=melding;
 
   if ( veld.value != "" && veld.value != " " && veld.value != "  " && veld.value.length >= minimumlength)
    {return true }
   else
    {alert(veldnaam+" is niet goed ingevuld.");
     veld.focus();
     veld.select();
     return false}
}//function checkName

function checkEmail(veld,melding)
{
 veldnaam=melding;
  invalidChars = " /:,;"
  emailveldvalid=true;
  if (veld.value == "") {// cannot be empty
    emailveldvalid=true;}
  else
  {
    for (i=0; i<invalidChars.length; i++) {// does it contain any invalid characters?
      badChar = invalidChars.charAt(i)
      if (veld.value.indexOf(badChar,0) > -1) {
        emailveldvalid=false;
      }
    }
    atPos = veld.value.indexOf("@",1)	// there must be one "@" symbol
    if (atPos == -1) {
      emailveldvalid=false;
    }
    if (veld.value.indexOf("@",atPos+1) != -1) {	// and only one "@" symbol
      emailveldvalid=false;
    }
    periodPos = veld.value.indexOf(".",atPos)
    if (periodPos == -1) {					// and at least one "." after the "@"
      emailveldvalid=false;
    }
    if (periodPos+3 > veld.value.length)	{		// must be at least 2 characters after the "."
      emailveldvalid=false;
    }
  }

   if (emailveldvalid)
    { return true }
   else { alert(veldnaam+" is niet goed ingevuld.");
    veld.focus();
    veld.select();
    return false}
}//function checkEmail

function checkFields(formulier) {
  if (checkName(formulier.naam_postcodecijfers,"Postcodecijfers",4) ) {
    if (checkName(formulier.naam_voetafdruk,"Voetafdruk",1) ) {
      if (checkEmail(formulier.naam_email,"E-mail")) {
        formulier.submit();
      }
    }
  }
}//function checkfields