[RESOLVED] Code Broke when I added the Ajax request.

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

    var taskInput = document.getElementById("new-task"); //new-task
    var addButton = document.getElementsByTagName("button")[0]; //first-button
    var incompleteTasksHolder = document.getElementById("incomplete-tasks"); //incomplete-tasks
    var completedTasksHolder = document.getElementById("completed-tasks"); //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");
        //Label
      var label = document.createElement("label");
        //Input (text)
      var editInput = document.createElement("input");
        //button.edit
      var editButton = document.createElement("button");
        //button.delete
      var deleteButton = document.createElement("button");
        //each element, needs modifying and appending

      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;
    }

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

      taskInput.value = "";

    }

    //Edit an Existing task
    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 from editMode
          //label text becomes input value
        label.innerText = editInput.value;
      } else {
        //else
          //Switch to editMode
          //Input value becomes label's text
        editInput.value = label.innerText;
       }

        //Toggle .editMode on the parent
      listItem.classList.toggle("editMode");

    }
    //Delete an existing task
    var deleteTask = function() {
      console.log("Delete task...");
      //remove the parent list item from the ul
      var listItem = this.parentNode;
      var ul = listItem.parentNode;
      ul.removeChild(listItem);

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

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

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

        //bind deleteTask to delete button
      deleteButton.onclick = deleteTask;

        //bind checkBoxEventHandler to checkbox
      checkBox.onchange = checkBoxEventHandler;

    }

    var ajaxRequest = function() {
      console.log("AJAX Request");
    }

    //Set the click handler to the addTask function
    addButton.addEventListener = ("click", addTask);
    addButton.addEventListener = ("click", ajaxRequest);

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

    //cycle over the completedTasksHolder ul li items
    for (var i = 0; i < completedTasksHolder.children.length; i++) {
      bindTaskEvents(completedTasksHolder.children[i], taskIncomplete);
    }
      //for each list item
        //bind events to list item's children (taskIncomplete)