sessionStorage未按预期工作 [英] sessionStorage isn't working as expected

问题描述

这是我的代码：

    sessionStorage.loggedIn = true;

    if (sessionStorage.loggedIn) {
        alert('true');
    }
    else {
        alert('false');
    }

足够简单。必须有一些小事我不了解JavaScript如何评估这些表达式。当我输入 sessionStorage.loggedIn = false 时，false警告会正确显示。但是，当我将 sessionStorage.loggedIn 更改为true时，即使清除会话后，false警报仍会弹出。我对这个表达的态度是什么？看起来很简单，也许我只需要另外一双眼睛。

Simple enough. There must be some small thing I'm not understanding about how JavaScript is evaluating these expressions. When I put sessionStorage.loggedIn = false, the "false" alert shows correctly. However, when I change sessionStorage.loggedIn to true, the "false" alert still pops, even after clearing the session. What am I not getting right with this expression? It seems so simple, maybe I just need another pair of eyes on it.

推荐答案

尝试将代码更改为

sessionStorage.setItem('loggedIn',JSON.stringify(true));

if (JSON.parse(sessionStorage.getItem('loggedIn'))) {
    alert('true');
}
else {
    alert('false');
}

它应该在所有主流浏览器中保持一致。

and it should work consistently across all major browsers.

具有 setItem / getItem 方法的接口是规范的编写方式，所以这样比使用分配属性的快捷方式更安全。此外， sessionStorage ，如 localStorage 是一个基于文本的存储机制，并不意味着存储对象，所以你需要换行使用 JSON.parse 和 JSON.stringify 进行调用，以全面获得预期结果。

The interface with the setItem/getItem methods is how the spec is written, so going that way is safer than using the shortcut of assigning properties. Also, sessionStorage, like localStorage is a textbased storage mechanism, and not meant for storing objects, so you need to wrap calls with JSON.parse and JSON.stringify to get the expected results across the board.

请注意 JSON.parse 对于undefined / null值并不总是很好，所以做一些类型检查可能是明智的首先。

Be aware that JSON.parse doesn't always play nice with undefined/null values, so it might be wise to do some type checking first.

您可以在此处阅读存储界面的规范

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