Getting 'Nan'?

var xhr = new XMLHttpRequest();

xhr.onreadystatechange = function () {
  if (xhr.readyState === 4) {

    var employees = JSON.parse(xhr.responseText);
    var statusHTML = '<ul class="bulleted">';

    for (var i = 0; i < employees.length; i += 1) {

      if (employees[i].inoffice == true) {
        statusHTML +='<li class="in">';
      } 
      else {
        statusHTML += '<li class="out">';
      }

      statusHTML += employees[i].name;
      statusHTML += '</li>';
    }
    statusHTML =+ '</ul>'

    document.getElementById('employeeList').innerHTML = statusHTML;

  } 
};


xhr.open('GET', 'data/employees.json');

xhr.send();