function contactForm(formName, subjectName, textareaName) {
  this.txtSubject = document[formName][subjectName];
  this.txtArea = document[formName][textareaName];
}

contactForm.prototype = {
  chkForm: function() {
    var formSubject = this.txtSubject.value;
    var formText = this.txtArea.value;
    var flag = true;
    if (formSubject == '') {
      alert('お問い合わせ件名をご記入ください。');
      flag = false;
    } else if (formText == '') {
      alert('お問い合わせ内容をご記入ください。'); 
      flag = false;
    }
    if (flag) {
      location.href = "mailto:" + EscapeSJIS('info@infovision.co.jp') + "?subject=" + EscapeSJIS(formSubject) + "&body=" + EscapeSJIS(formText);
    }
  }
}