Checkbox, Edit and Delete buttons not functional on newly created items

// TODO
// Problem: Add, Delete and checkbox doesn't work on newly created items

var taskInput = document.getElementById("new-task"); // #new-task
var addButton = document.getElementsByTagName("button")[0]; // first button in the DOM
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"); //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 element needs modifying

    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 - similar to function addTask();
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]"); //return the first one selector (querySelectorAll needs an index sinon)
    var label = listItem.querySelector("label");

    var containsClass = listItem.classList.contains("editMode");
        // if the class of the parent is .editMode
        if(containsClass) {
            // switch from editMode
            // make the label text become the input's value
            label.innerText = editInput.value;
        } else {
            // switch to editMode
            // input value becomes the label text
            editInput.value = label.innerText;
        }

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

}

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

        // remove the li (parent of button) from the ul (grandparent)
        ul.removeChild(listItem);

}

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

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

var bindTaskEvents = function(taskListItem, checkBoxEventHandler) {
        console.log( "bind list item event..." );
        // 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 taskCompleted to the checkbox
        checkBox.onchange = checkBoxEventHandler;
}


// Set the click handler to the Add task function
addButton.onclick = addTask; // no the call of the function (missing () but just a reference )

// loop over the incompleteTaskHolder ul list items
for (var i = 0; i < incompleteTasksHolder.children.length; i++) {
    // bind taskCompleted to the checkbox
    bindTaskEvents( incompleteTasksHolder.children[i], taskCompleted );
}


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