JavaScript 中是否有用于检查对象属性的“not in”运算符？
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原文地址: http://stackoverflow.com/questions/7972446/
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Is there a “not in” operator in JavaScript for checking object properties?
提问by Aaron
Is there any sort of "not in" operator in JavaScript to check if a property does not exist in an object? I couldn't find anything about this around Google or Stack Overflow. Here's a small snippet of code I'm working on where I need this kind of functionality:
JavaScript 中是否有任何类型的“不在”运算符来检查对象中是否不存在属性？我在 Google 或 Stack Overflow 上找不到任何关于此的信息。这是我正在处理需要这种功能的一小段代码：
var tutorTimes = {};
$(checked).each(function(idx){
id = $(this).attr('class');
if(id in tutorTimes){}
else{
//Rest of my logic will go here
}
});
As you can see, I'd be putting everything into the elsestatement. It seems wrong to me to set up an if–elsestatement just to use the elseportion.
如您所见，我会将所有内容都放入else声明中。在我看来，为了使用该部分而设置if-else语句似乎是错误的else。
回答by Jord?o
It seems wrong to me to set up an if/else statement just to use the else portion...
设置 if/else 语句只是为了使用 else 部分对我来说似乎是错误的......
Just negate your condition, and you'll get the elselogic inside the if:
只需否定你的条件，你就会得到else里面的逻辑if：
if (!(id in tutorTimes)) { ... }
回答by some
As already said by Jord?o, just negate it:
正如 Jord?o 已经说过的那样，只需否定它：
if (!(id in tutorTimes)) { ... }
Note: The above test if tutorTimes has a property with the name specified in id, anywherein the prototype chain. For example "valueOf" in tutorTimesreturns truebecause it is defined in Object.prototype.
注意：以上测试是否tutorTimes在原型链中的任何位置具有id 中指定的名称的属性。例如"valueOf" in tutorTimes返回true因为它是在Object.prototype 中定义的。
If you want to test if a property doesn't exist in the current object, use hasOwnProperty:
如果要测试当前对象中是否不存在某个属性，请使用 hasOwnProperty：
if (!tutorTimes.hasOwnProperty(id)) { ... }
Or if you might have a key that is hasOwnProperyyou can use this:
或者，如果您可能有一个hasOwnPropery密钥，您可以使用它：
if (!Object.prototype.hasOwnProperty.call(tutorTimes,id)) { ... }
回答by Forage
Personally I find
个人觉得
if (id in tutorTimes === false) { ... }
easier to read than
比阅读更容易
if (!(id in tutorTimes)) { ... }
but both will work.
但两者都会起作用。
回答by reedlauber
Two quick possibilities:
两种快速的可能性：
if(!('foo' in myObj)) { ... }
or
或者
if(myObj['foo'] === undefined) { ... }
