label has a value of undefined

var taskInput = document.getElementById('new-task'); //new-task
var addButton = document.getElementsByTagName('button')[0]; //first button on page
var incompleteTasksHolder = document.getElementById('incomplete-tasks'); //incomplete-tasks
var completedTasksHolder = document.getElementById('completed-tasks'); //completed-tasks



var createNewTaskElement = function(taskString){

  var listItem = document.createElement("li");
  var checkBox = document.createElement("input");

  var label = document.createElement("label");

  var editInput = document.createElement("input");

  var editButton = document.createElement("button");

  var deleteButton = document.createElement("button");


  checkBox.type = "checkbox";
  editInput.type = "text";

  editButton.innerText = "Edit";
  editButton.className = "edit";
  deleteButton.innerText = "Delete";
  deleteButton.className = "delete";

  label.innerText = taskString;


  listItem.appendChild(checkBox);
  listItem.appendChild(label);
  listItem.appendChild(editInput);
  listItem.appendChild(editButton);
  listItem.appendChild(deleteButton);

  return listItem;
};

var addTask = function(taskInput){
  console.log("Add task..");

  var listItem = createNewTaskElement(taskInput.value);

  incompleteTasksHolder.appendChild(listItem);
  bindTaskEvents(listItem, taskCompleted);
};


var editTask = function(){
  console.log("Edit task..");


};



var deleteTask = function(){
  console.log("Delete task..");
    var listItem = this.parentNode;
    var ul = listItem.parentNode;

    ul.removeChild(listItem);
};



var taskCompleted = function(){
  console.log("Task Complete..");

    var listItem = this.parentNode;
    completedTasksHolder.appendChild(listItem);
    bindTaskEvents(listItem, taskIncomplete);
};



var taskIncomplete = function(){
  console.log("Task Incomplete..");

    var listItem = this.parentNode;
    incompleteTasksHolder.appendChild(listItem);
    bindTaskEvents(listItem, taskCompleted);
};

var bindTaskEvents = function(taskListItem, checkBoxEventHandler){
  console.log("Bind list items events");

  var checkBox = taskListItem.querySelector("input[type=checkbox]") ;
  var editButton = taskListItem.querySelector("button.edit");
  var deleteButton = taskListItem.querySelector("button.delete");

    editButton.onclick = editTask;

    deleteButton.onclick = deleteTask;

    checkBox.onchange = checkBoxEventHandler;
};


addButton.onclick = addTask;




for (var i=0; i< incompleteTasksHolder.children.length ; i++) {

    bindTaskEvents(incompleteTasksHolder.children[i], taskCompleted);
}


for (var i=0; i< completedTasksHolder.children.length ; i++) {

    bindTaskEvents(completedTasksHolder.children[i], taskIncomplete);
}