JSON对象返回未定义的值 [英] JSON object returns undefined value

问题描述

我从http调用接收到JSON对象，并且试图从中提取值. JSON对象包含:

I am receiving a JSON object from a http call and I am trying to extract values from it. JSON object contains:

data:{"userid":"007", "role":"spy"}

我使用以下代码将角色属性分配给另一个变量，然后进行一些控制台日志检查:

I use the following code to assign role property to another variable followed by some console log checks:

    currentUserRole = data.role;    
    console.log("type of data: "+typeof(data));
    console.log("data: "+JSON.stringify(data));
    console.log("user role: "+currentUserRole);

日志产生:

type of data: object
data: [{"userid":"007", "role":"spy"}]
user role: undefined

我还尝试了另一种赋值方法:

Also I tried another method of assignment:

currentUserRole = data['role'];

但是currentUserRole仍然未定义.如何将JSON对象的属性设置为变量?

But currentUserRole remains undefined. How can I set a property of a JSON object to a variable?

推荐答案

根据日志的第二行(对JSON.stringify()的调用)，您的data实际上是 array 的对象:

According to the second line of your log (the call to JSON.stringify()), your data is actually an array of objects:

[{"userid":"007", "role":"spy"}]

如果它是您所期望的对象，它将看起来像这样:

If it was an object as you are expecting, it would look like this:

{"userid":"007", "role":"spy"}

(差异很小，但请注意缺少方括号)

(the difference is subtle, but notice the missing square brackets)

尝试一下:

currentUserRole = data[0].role;

很显然，在生产就绪型代码中，您可能需要做一些额外的健全性检查，以确保data实际上是一个至少包含一个元素的数组.

Obviously in production-ready code, you probably need to do some extra sanity checking to ensure that data is in fact an array containing at least one element.

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