typescript 从本地存储保存和检索日期
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Saving and retrieving Date from local storage
提问by Programmer1994
This may seem like a silly question but I'm having a rather difficult time, understanding Typescript. I have following code:
这似乎是一个愚蠢的问题，但我很难理解 Typescript。我有以下代码：
var date = new Date();
window.localStorage.setItem("date", date);
As you see, I'm generating todays date and store it via local storage. Now I want to retrieve this value inside another function, add 7 days to it, store it again, and show the new value in an alert-box.
如您所见，我正在生成今天的日期并通过本地存储进行存储。现在我想在另一个函数中检索这个值，向它添加 7 天，再次存储它，并在警报框中显示新值。
var date = window.localStorage.getItem("date");
date.setDate(date.getDate() + 7);
window.localStorage.setItem("date", date);
alert(date);
When I run this code, it keeps telling me Undefined is not a functionon the second rule of the second code-block (probably the .getDate() function).
当我运行这段代码时，它不断告诉我Undefined is not a function第二个代码块的第二条规则（可能是 .getDate() 函数）。
Someone who knows what I might be doing wrong? I thought this simple piece of javascript would run fine in typescript without changing the code...
有人知道我可能做错了什么吗？我认为这段简单的 javascript 可以在打字稿中正常运行而无需更改代码...
回答by Lloyd Banks
Everything put into localStorage is stored as a string. Your date is originally an object. You need to convert the string back to an object after you get the value from localStorage.
放入 localStorage 的所有内容都存储为字符串。您的日期最初是一个对象。从 localStorage 获取值后，您需要将字符串转换回对象。
var date = window.localStorage.getItem("date");
// Initialize the date object as a date object again here
date = new Date(date);
date.setDate(date.getDate() + 7);
回答by taxicala
You should store the timestamp in localStorage, and then retreive it, create a new Date with that timestamp, add 7 days, and then store it again:
您应该将时间戳存储在 localStorage 中，然后检索它，使用该时间戳创建一个新的 Date，添加 7 天，然后再次存储它：
var date1 = new Date();
window.localStorage.setItem("date", date.getTime());
var date2 = new Date(window.localStorage.getItem("date"));
date2.setDate(date2.getDate() + 7);
window.localStorage.setItem("date", date2.getTime());
alert(date2);
回答by Nathan Merrill
If you perform the following
如果您执行以下操作
var date = new Date();
window.localStorage.setItem("date", date);
var date1 = window.localStorage.getItem("date");
console.log(date1)
You will find that date1is a string. This is because localStorage stores all of its data as strings.
你会发现那date1是一个字符串。这是因为 localStorage 将其所有数据存储为字符串。
You should parse the string by creating a new Date with the returned string.
您应该通过使用返回的字符串创建一个新的 Date 来解析字符串。
