addevent侦听器 购物车不起作用

我会保持简单，在我的jsfiddle中，我有一个使用javascript的购物车。我想要的是有人点击按钮，它会将商品添加到购物车中。不幸的是，该函数不会调用AdditemtoCart，除非它在让我发疯的函数之外。让我知道我做错了什么。

JSFIDDLE 链接 ： https://jsfiddle.net/w2z3rb9h/51/

<div  id="cart" class="glyphicon glyphicon-shopping-cart">
<div id="money">
$</div>
<div id="length">
Items
</div>
</div>
<button name="button" id="addItem">
Add Item
</button> 
HTML Code above
// [(START)Cart]-------->
var cart = [];
// [(END)Cart]---------->

// [(START)Factory]-------->
var Item = function(name, price, count) {
    this.name = name;
    this.price = price;
    this.count = count;
};
// [(END)Cart]-------------->

// [(START)Adding Items to Cart]-------->
function addItemToCart(name, price, count){
for (var key in cart) {
 if (cart[key].name === name) {
         cart[key].count += count;
         cart[key].price += price;
         return;
     }
}
var item = new Item(name, price, count);
cart.push(item);
}
// [(END)Adding Items to Cart]---------->

// [(START)Remove Item From Cart]-------->
function removeItemFromCart(name,price) {
 for(var key in cart) {
     if(cart[key].name === name) {
        cart[key].count --;
        cart[key].price -= price;
     if(cart[key].count === 0) {
        cart.splice(key,1);
     }
        break;
     } 
 }
}
// [(END)Remove Item From Cart]-------->

// [(START)Remove All Item From Cart]-->
function removeItemFromCartAll(name){
  for (var key in cart){
      if(cart[key].name === name){
      cart.splice(key, 1);
      break;
      }
  }
}
// [(END)Remove All Item From Cart]---->

function call() {
addItemToCart("Apple", 1.2, 1);
 alert("It works");
}

document.getElementById("addItem").addEventListener("mousedown", call);

// [(START)Get Cart Amount] ----------->
function cartlength() {
var x = 0;
for (var key in cart) {
  x += cart[key].count;
}
 document.getElementById("length").innerHTML  = "Items:" + x;
}
//Invoked:Get Cart Amount
cartlength();
// [(END)Get Cart Amount] ----------->

// [(START)Price] ------------------->
function cartprice() {
var y = 0;
for (var key in cart) {
  y += cart[key].price;
}
 document.getElementById("money").innerHTML  = "$" + y;
}
//Invoke: Price
cartprice();
// [(END)Price] --------------------->