Chrome Cookie API不允许我使用返回的值 [英] Chrome Cookie API isn't letting me use returned values

问题描述

我正在做一个chrome扩展，在用户登录时设置一个cookie。当我尝试使用 chrome.cookies.get（）方法读取cookie的回调可以记录结果，但我不能将它从回调中传递。

I am making a chrome extension which sets a cookie when users log in. When I attempt to read the cookie using the chrome.cookies.get() method the callback can log the results but I cant pass it out of the callback.

function getCookie (cookieName){
    var returnVal; 
    chrome.cookies.get({
        'url':'https://addictedtogether.com/',
        'name':cookieName
    },
    function(data){
        console.log(data); //log displays returned cookie in a object
        returnVal=data;
    }
    );
    console.log(returnVal);  //log says this is undefined
    return returnVal;
}

我尝试使用两种不同的方式传递结果，除非从回调中调用，否则对象是未定义的。

I tried using a couple different ways of passing the result but it seems like the object is undefined unless it is called from within the callback.

推荐答案

问题是你的回调在主函数返回。 （扩展API被称为异步的原因！） returnVal 是未定义的，因为它还没有被分配到。尝试修改函数以接受回调参数：

The problem is that your callback is called after the main function returns. (The extension APIs are called asynchronous for a reason!) returnVal is undefined because it hasn't been assigned to yet. Try modifying your function to accept a callback argument:

function getCookie (cookieName, callback){
    chrome.cookies.get({
        'url':'https://addictedtogether.com/',
        'name':cookieName
    },
    function(data){
        callback(data);
    });
}

// Use like this:
getCookie("CookieName", function(cookieData){
  // Do something with cookieData
});

如果你不喜欢传递回调，你也可以修改你的函数返回一个延迟。如果你必须处理很多异步函数调用，延迟使你的生活更容易。下面是一个使用jQuery.Deferred的例子：

If you don't like passing callbacks around, you could also modify your function to return a deferred. If you have to handle a lot of asynchronous function calls, deferreds make your life a lot easier. Here's an example using jQuery.Deferred:

function getCookie (cookieName){
    var defer = new jQuery.Deferred();
    chrome.cookies.get({
        'url':'https://addictedtogether.com/',
        'name':cookieName
    },
    function(data){
        defer.resolve(data);
    });
    return defer.promise();
}
// Example use:
getCookie("FooBar").done(function(data){
  // Do something with data
});

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