When I try to create a new task the value is output as taskString and I don't know why.

// Problem: User Interaction doesn't provide desired results.
// Solution: Add interactivity so the user can manage daily tasks.


var taskInput = document.getElementById("new-task"); //news-task
var addButton = document.getElementsByTagName("button")[0]; //first-button
var incompleteTaskHolder = document.getElementById("incomplete-tasks"); //incomplete-tasks
var completedTaskHolder = document.getElementById("completed-tasks");

// New Task List Item
var createNewTaskElement = function(taskString) {

  // Create list item
  var listItem = document.createElement("li");

  // Input (checkbox)
  var checkBox = document.createElement("input"); //checkbox

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

  // Input (text)
  var editInput = document.createElement("input"); //text

  // Button.edit
  var editButton = document.createElement("button");

  // Button.delete
  var deleteButton = document.createElement("button");

  // Each elements needs modifiying.

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

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

  label.innerText = "taskString"


  // Each element needs appending
  listItem.appendChild(checkBox);
  listItem.appendChild(label);
  listItem.appendChild(editInput);
  listItem.appendChild(editButton);
  listItem.appendChild(deleteButton);
  return listItem;
}

// Add a new task.

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

  // Create a new list item with the text from #new-task:
  var listItem = createNewTaskElement(taskInput.value);

  //Append listItem to incompleteTaskHolder
  incompleteTaskHolder.appendChild(listItem);
  bindTaskEvents(listItem, taskCompleted);

}

// Edit an existing taks.
var editTask = function() {
  console.log("Edit Task...");

  var listItem = this.parentNode;

  var editInput = listItem.querySelector("input[type=text]");
  var label = listItem.querySelector("label");


  var containsClass = listItem.classList.contains("editMode");
  // if the class of the parent is .editMode
  if(containsClass) {
    // Switch form .editMode
    // Label text become the input's value
    label.innerText = editInput.value;
  } else {
    // Switch to .editMode
    // Input value becomes the label's text
    editInput.value = label.innerText;
  }
// Toggle .editMode on the list item

  listItem.classList.toggle("editMode");
}

// Delete an existing task.
var deleteTask = function() {
  console.log("Delete Task...");

  var listItem = this.parentNode;
  var ul = listItem.parentNode;

  // Remove the parent list item from the ul
  ul.removeChild(listItem);

}

// Mark a Task as complete.
var taskCompleted = function() {
  console.log("Task Complete...");
    //Append the task list item to the #completed-tasks
  var listItem = this.parentNode
  completedTaskHolder.appendChild(listItem);
  bindTaskEvents(listItem, taskIncomplete);
}


// Mark a task as incomplete.
var taskIncomplete = function() {
  console.log("Task Incomplete...");
    //Append the list item to the #incomplete-tasks
  var listItem = this.parentNode
  incompleteTaskHolder.appendChild(listItem);
  bindTaskEvents(listItem, taskCompleted);
}

var bindTaskEvents = function(taskListItem, checkBoxEventHandler) {
  console.log("Bind list item events");
    // Select it's children
    // bind the editTask to edit button
    // bind the deleteTask to the delete button
    // bind checkBoxEventHandler to the checkbox
}

var bindTaskEvents = function(taskListItem, checkBoxEventHandler) {
  console.log("Bind list item events");
    // Select taskListItem's children
  var checkBox = taskListItem.querySelector("input[type=checkbox]");
  var editButton = taskListItem.querySelector("button.edit");
  var deleteButton = taskListItem.querySelector("button.delete");
    // bind the editTask to edit button
  editButton.onclick = editTask;
    // bind the deleteTask to the delete button
  deleteButton.onclick = deleteTask;
    // bind taskCompleted to checkbox
  checkBox.onchange = checkBoxEventHandler;
}

// Set the click handler to the addTask function

addButton.onclick = addTask;

// cycle over incompleteTaskHolder ul list items
for(var i = 0; i < incompleteTaskHolder.children.length; i++) {
    // Bind events to list item's children (taskCompleted)
  bindTaskEvents(incompleteTaskHolder.children[i], taskCompleted);
}

// cycle over completeTaskHolder ul list items
for(var i = 0; i < completedTaskHolder.children.length; i++) {
    // Bind events to list item's children (taskIncomplete)
  bindTaskEvents(completedTaskHolder.children[i], taskIncomplete);
}