无法在 localStorage 的数组中推送对象

Question

我正在尝试将 localStorage 值存储在数组中并关注此页面 Push JSON Objects to array in localStorage。我的代码是：

function SaveDataToLocalStorage(data)
{
 var a = [];
 // Parse the serialized data back into an aray of objects
 a = JSON.parse(localStorage.getItem('session'));
 // Push the new data (whether it be an object or anything else) onto the array
 a.push(data);
 // Alert the array value
 alert(a);  // Should be something like [Object array]
 // Re-serialize the array back into a string and store it in localStorage
 localStorage.setItem('session', JSON.stringify(a));
}

data 在哪里：

 var data = {name: "abc", place: "xyz"}

我收到以下错误：

 Uncaught TypeError: Cannot call method 'push' of null 

谁能展示在数组中存储 localStorage 值的正确方法？

Answer 1

当您获取本地存储内容时，您将覆盖初始化“a”的初始空数组。变量被声明和初始化：

var a = [];

然后那个空数组立即被扔掉：

a = JSON.parse(localStorage.getItem('session'));

之后，如果您收到该错误，您检索到的值实际上是空的 (null)。

如果您希望“a”是或者一个新的空数组，或者是保存在本地存储中的数组，您可以这样做：

var a = localStorage.getItem('session') || "[]";
a = JSON.parse(a);

Answer 2

null 是未初始化为任何对象的特殊值。 我的猜测是 localStorage.getItem('session') 是空的。

一个更可靠的答案是这样的

function SaveDataToLocalStorage(data)
{
    var a;
    //is anything in localstorage?
    if (localStorage.getItem('session') === null) {
        a = [];
    } else {
         // Parse the serialized data back into an array of objects
         a = JSON.parse(localStorage.getItem('session'));
     }
     // Push the new data (whether it be an object or anything else) onto the array
     a.push(data);
     // Alert the array value
     alert(a);  // Should be something like [Object array]
     // Re-serialize the array back into a string and store it in localStorage
     localStorage.setItem('session', JSON.stringify(a));
}