javascript - 检查Javascript中的字段是否为空或未定义（而不是零或空字符串）的常用方法是什么？(What's the common way to check if a field is null or undefined (but not zero or empty string) in Javascript?)

Question

I know I can't do if (!obj.x) because if obj.x is 0 or "" , it will be "truthy".

(我知道if (!obj.x)不能执行if (!obj.x)因为如果obj.x为0或"" ，它将是“真实的”。)

Option 1: I could do if (obj.x === null || obj.x === undefined) .

(选项1： if (obj.x === null || obj.x === undefined)我可以做。)

Option 2: But could I just do if (obj.x == null) ?

(选项2：但是， if (obj.x == null)我可以做吗？)

Just to be clear, I want a condition that is true when obj.x is null or undefined , but false for any other value.

(为了清楚obj.x ，我想要一个条件，当obj.x为null或undefined时为true，但对于其他任何值obj.x false。)

According to the comments, both options are equivalent but option 2 is more clear.

(根据评论，这两个选项是等效的，但选项2更清晰。)

I agree.

(我同意。)

EDIT:

(编辑：)

Someone pointed out that there are similar questions (see links above), but in this case I was thinking of fields, rather than variables.

(有人指出存在类似的问题（请参阅上面的链接），但是在这种情况下，我在考虑字段而不是变量。)

The difference is that fields can be undefined and there is no runtime error when using them.

(区别在于字段可以是undefined并且使用它们时没有运行时错误。)

I updated my question accordingly.

(我相应地更新了我的问题。)

EDIT 2:

(编辑2：)

This question was closed because there are similar questions.

(因为存在类似的问题，所以已关闭此问题。)

I think there is a slight difference here, because in my question I'm checking a field/property of an object, not a variable.

(我认为这里有细微的差别，因为在我的问题中，我要检查的是对象的字段/属性，而不是变量。)

For properties, it's more common to check for undefined than for variables, where checking for undefined is quite rare.

(对于属性，检查undefined比检查变量更常见，在这种情况下，检查undefined非常罕见。)

Actually, it doesn't make sense to check variable === undefined since it would throw an error when the variable is undefined.

(实际上，检查variable === undefined毫无意义，因为当变量未定义时会抛出错误。)

  ask by Ferran Maylinch translate from so

Answer 1

等待大神答复