Before getting into the details of how your application is going to work, you should connect all the buttons up to “dummy” functions, to make testing them easier.
From the Beginner JavaScript Sushi Cards, you will hopefully remember that a JavaScript function definition looks like this:

function newToDoItem(itemText, completed) {
   alert("New item created: "+itemText+"  Completed state: "+completed);
}

Almost all the functions you need are in the file already, though they don't do anything cool yet. They just send alert messages (pop-up boxes) telling you what function was called and what the values in the parameters were. Read through them to understand what's there.

There's one missing, that you need to add. Create a new function in to-do.js that:

• Is called toggleToDoItemState
• Accepts a parameter: listItem
• When called, alerts the message "Toggling state of item "+itemId

Now you need to tell JavaScript to listen for a click on the buttons, then do something. Each of the buttons on the page has a unique id. You can use that id to tell JavaScript what to listen to. Add the following code instead of the alert into the runWhenPageLoads function:

 document.getElementById("add-button").addEventListener("click", addToDoItem)

Because runWhenPageLoads is called at the end of the file, and the file is loaded at the end of the HTML page, runWhenPageLoads will, as you might guess, run once the page loads! This bit of code chains together a lot of functions with dots (.), where each function's is acting on the thing fetched by the function before it:

• Look in the document—the whole page
• Find the element (HTML tag) on that page that has “add-button” as its id
• Tell JavaScript to listen for the click action on the button and then run the addToDoItem function whenever it “hears” the action

Reload index.html and click the button that says “Add”. You should see an alert message pop up! Do the same for the other two buttons:

• Connect #clear-button to clearCompletedToDoItems
• Connect #empty-button to emptyList

Don't forget to test them!