如何從sessionStorage檢索對象？

Question

我正在生成菜餚（是對象）的列表，當用戶單擊按鈕時，InitializeFoodList（）應該將選定的項目添加到sessionStorage。 然后在RetrieveDataFromCart（）中，我想遍歷sessionStorage並在控制台中顯示所有這些項目。

問題是最終結果是item屬性為null或僅顯示最后添加的項，而下一個為null。

有人知道實現此目標的更好方法嗎？

 var list = [{ id: 1, name: "Spaghetti", price: 15, category: "main", pictureSrc: "images/food/spaghetti.jpg" }, { id: 2, name: "Lasagne", price: 20, category: "main", pictureSrc: "images/food/Lasagne.jpg" }, { id: 3, name: "Coca-cola", price: 5, category: "drinks", pictureSrc: "images/food/cola.jpg" }, { id: 4, name: "Chicken", price: 12, category: "main", pictureSrc: "images/food/chicken.jpg" }, ]; function InitializeFoodList() { var foodList = $('#foodList'); for (let i = 0; i < list.length; i++) { const element = list[i]; var buttonText = '<button class="btn btn-primary add" id="add' + i + '">+</button><button class="btn btn-primary" name="remove">-</button>'; foodList.append("<li class='list-inline-item'><h4>" + element.name + "</h4><p>" + element.price + " zł</p><img alt=''height='200' width='200' class='img-thumbnail' src='" + element.pictureSrc + "'><br>" + buttonText + "</li>"); $('#add' + i).click(function() { sessionStorage.setItem("cart", JSON.stringify(element)); }); } } function RetrieveDataFromCart() { var elements = []; for (let i = 0; i < sessionStorage.length; i++) { var element = JSON.parse(sessionStorage.getItem(localStorage.key(i))); elements.push(element); console.log(element.name); } } 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <div> <button onclick="InitializeFoodList()">Click me</button> <button onclick="RetrieveDataFromCart()">Retrieve</button> <ul id="foodList" class="list-inline"></ul> </div> 

Answer 1

我只是將整個陣列保存在一個鍵下

然后，您可以在內存中的數組中添加/刪除或修改對象，並在每次更改數組時存儲修改后的數組

function getStoredCart(){
    // return stored array and if not existing return an empty array
    return JSON.parse(sessionStorage.getItem('cart') || '[]')
}

function saveCart(array){
   sessionStorage.setItem("cart", JSON.stringify(array)); 
}

// example deleting item
function deleteItem(item){
    var itemIndex = cartList.indexOf(item)
    cartArray.splice(itemIndex,1); // remove from stored array       
    saveCart(cartArray ); // save it back into storage
}

// example adding item
function addItem(itemObject){       
    cartArray .push(itemObject); // push new object to array       
    saveCart(cartArray ); // save it back into storage
}


// keep array reference in variable whole time page is active
var cartArray = getStoredCart();

$.each(cartArray , function(i, item){
    // add the html for each item and use `item` reference in click handlers when doing modifications
})

Answer 2

您正在正確使用sessionStorage，但是此代碼段中存在一些問題。 首先，在sessionStorage中設置項目時，您每次都會添加“購物車”作為鍵，這樣會導致覆蓋存儲在sessionStorage中的項作為鍵值對存儲的先前值，並且鍵應該是唯一的，否則它會更新存儲在相同的鍵。

因此，我使用鍵名'cart'即'cart'+ i添加了i的值。 您可以根據用例使用任何唯一鍵。 其次，與其使用localStorage來獲取特定的密鑰，不如使用會話存儲（似乎有些錯字）

更新的代碼段

var list = [{
    id: 1,
    name: "Spaghetti",
    price: 15,
    category: "main",
    pictureSrc: "images/food/spaghetti.jpg"
},
{
    id: 2,
    name: "Lasagne",
    price: 20,
    category: "main",
    pictureSrc: "images/food/Lasagne.jpg"
},
{
    id: 3,
    name: "Coca-cola",
    price: 5,
    category: "drinks",
    pictureSrc: "images/food/cola.jpg"
},
{
    id: 4,
    name: "Chicken",
    price: 12,
    category: "main",
    pictureSrc: "images/food/chicken.jpg"
},
];

function InitializeFoodList() {

var foodList = $('#foodList');

for (let i = 0; i < list.length; i++) {
    const element = list[i];
    var buttonText = '<button class="btn btn-primary add" id="add' + i + '">+</button><button class="btn btn-primary" name="remove">-</button>';
    foodList.append("<li class='list-inline-item'><h4>" + element.name + "</h4><p>" + element.price + " zł</p><img alt=''height='200' width='200' class='img-thumbnail' src='" + element.pictureSrc + "'><br>" + buttonText + "</li>");
    $('#add' + i).click(function() {
    sessionStorage.setItem("cart" + i, JSON.stringify(element));
    });
}
}

function RetrieveDataFromCart() {

var elements = [];

for (let i = 0; i < sessionStorage.length; i++) {
    var element = JSON.parse(sessionStorage.getItem(sessionStorage.key(i)));
    elements.push(element);
    console.log(element.name);
}

}