Why aren't my querySelectors working?

//Problem: User interaction doesnt provide desired results
//Solution: Add interactivity so the user can manage daily tasks

var taskInput = document.getElementById("new-task");
var addButton = document.getElementsByTagName("button")[0]; //First Button
var incompleteTasksHolder = document.getElementById("incomplete-tasks"); 
var completedTasksHolder = document.getElementById("completed-tasks"); 

var addTask = function() {
//Add a new task
  console.log("Add Task...");
  //When the button is pressed
    //Create a new list item from #new-task
        //input checkbox
        //label
        //input (text)
        //button .edit
        //button .delete
        // Each elements needs modified and appended
}

var editTask = function() {
//Edit an existing task
  console.log("Edit Task...");
    //When the edit button is pressed
        //if li is .editmode
            //Switch from .editmode
            //label text become input value
        //else
            //Switch to .editmode
            //input value becomes label's text

        //Toggle .editmode on the parent 
}


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

var taskCompleted = function() {
//Mark a task as complete
   console.log("Complete Task...");
    //When the checkbox is checked
      //Append the task list item to the #completed-tasks
}

var taskIncompleted = function() {
//Mark a task as incomplete
  console.log("IncompleteTask...");
  //When checkbox is unchecked
    //Append the list item to #incomplete-tasks
}

// WIRING 

var bindTaskEvents = function(taskListItem, checkBoxEventHandler) {
    console.log("Bind list items...");
    //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 the edit button
        editButton.onclick = editTask;
        //bind deleteTask to delete button
        deleteButton.onclick = deleteTask;
        //bind checkBoxEventHandler to checkbox

}

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

//cycle over incompleteTasksHolder ul list items
for (var i = 0; i < incompleteTasksHolder.children.length; i++) {
    //for each list item
        //bind events to list item's children (taskCompleted)
        bindTaskEvents(incompleteTasksHolder.children[1], taskCompleted);
}   

//cycle over completedTasksHolder ul list items
    for (var i = 0; i < completedTasksHolder.children.length; i++) {
    //for each list item
        //bind events to list item's children (taskIncompleted)
        bindTaskEvents(completedTasksHolder.children[1], taskIncompleted);
}