JSON.stringify（undefined）不是字符串

JSON.stringify(null) returns the string null.

JSON.stringify（null）返回字符串null。

JSON.stringify(undefined) returns the value undefined. Shouldn't it return the string undefined?

JSON.stringify（undefined）返回值undefined。它不应该返回字符串undefined吗？

Parsing the value undefined or the string undefined gives a SyntaxError.

解析未定义的值或未定义的字符串会产生SyntaxError。

Could someone explain why JSON chokes on undefined and how to get around it when stringifying / parsing values?

有人可以解释为什么JSON会在未定义时窒息，以及在字符串化/解析值时如何绕过它？

3 个解决方案

#1

undefined is not valid JSON, so the function is working properly.

undefined是无效的JSON，因此该函数正常工作。

http://en.wikipedia.org/wiki/JSON#Data_types.2C_syntax_and_example

#2

if(JSON.stringify(input) === undefined) {
    // error handle
}

要么

if(input === undefined) {
    // error handle
}
else {
    JSON.stringify(input);
}

Sorry. Life is hard sometimes. This is pretty much what you have to do.

抱歉。生活有时很难。这几乎是你必须要做的。

#3

The reason for this is that null is caused by a variable that doesn't have a value, so when converted to JSON it gives you JSON that doesn't have a value, undefined means it doesn't exist at all, so you can't create a JSON object of something that doesn't exist. Just check

原因是null是由没有值的变量引起的，所以当转换为JSON时，它会为你提供没有值的JSON，undefined意味着它根本不存在，所以你可以不要创建一个不存在的JSON对象。检查一下

 if(typeof myvar === 'undefined')

before you run it and handle the error gracefully in the code. Generally try to avoid undefined in your JS they can to weird things all over the place, and are NOT the same as null and are usually handled differently.

在运行它并在代码中正常处理错误之前。一般来说，尽量避免在JS中使用undefined，它们可能会在整个地方发生奇怪的事情，并且与null不同，并且通常以不同的方式处理。

#1