Attach an event handler on the form submission. On form submit add new list item to the end of
"ul#todo" with the value of "input#type-input". Reset the value of
"input#type-input" back to empty string.
Attach an event handler on the click event of "ul#todo". Handle click events on
individual list items and give them a css class of "done" when they are clicked on the first
time. Remove any list items that already have a class of "done" when they are clicked again.
The following can be helpful:
Document.getElementById(),
Document.querySelector(),
EventTarget.addEventListener(),
Event.preventDefault(),
Event.currentTarget,
Event.target,
Document.createElement(),
Node.removeChild(),
Element.tagName,
Element.classList , Element.classList.add(), Element.classList.remove(),
Element.classList.toggle(), and
Element.classList.contains()