Appends don't appear to be working

//Problem: User interaction does not provide desired results.
//Solution:Add interactivity so the user can accomplish daily tasks

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

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

      //Each element needs modified 

  // and each element needs  appended
  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 task: add a new <li> to <ul class="incomplete-tasks">
  var listItem = createNewTaskElement("Some New Task");
  //Append listeItem to incompleteTasksHolder;
  incompleteTasksHolder.appendChild(listItem);

}
//Edit an existing task
var editTask = function() {
  //When the edit button is pressed
  console.log("Edit task...");
    //If the class of the parent is .editMode
      //switch from .editMode
      //make label text become the input's value
    //else
      //switch to editMode
      //input value becomes the label's text

  //toggle /editMode
}

//Delete an existing task
var deleteTask = function(){
  console.log("delete task...");
  //When the delete button is pressed, 
    //remove the parent list item from the ul  
}

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


}

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

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 editTask to edit button
  editButton.onclick = editTask;
      //bind deleteTask to delete button
  deleteButton.onclick = deleteTask;
      //bind checkBoxEventHandler to the checkbox
  checkBox.onchange = checkBoxEventHandler;
}

//Set the click handler to the addTask function
addButton.onclick = addTask;

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

}

//Cycle over the completedTasksHolder ul list items
for(var i = 0; i < completedTasksHolder.children.length; i++) {
    bindTaskEvents(completedTasksHolder.children[i], taskIncomplete);
  }