// 1. Add jQuery's document.ready function

/* 2. Use jQuery to reference the elements by class,

add a click event and passing the corresponding function on the click */

// Start quantity at 0

var quantity = 0;

// JavaScript functions, no need to changes these

function addItem(){

quantity = quantity + 1;

refreshTotal();

}

function removeItem(){

if ( quantity > 0 ) {

quantity = quantity - 1;

} else {

// do nothing

}

refreshTotal();

}

function checkout() {

if ( quantity <= 0 ) {

alert( "Sorry, you don't have anything in your cart!" );

} else {

alert( "Thank you for your order!" );

}

}

function refreshTotal() {

// calculate the totalCost with a fixed price of $20.

var totalCost = quantity * 20;

// then update the quantity text field

document.getElementById('updateQuantity').value = quantity;

// update the total cost text field

document.getElementById('updateTotal').value = "$" + totalCost;

}