为什么空JavaScript数组在条件结构中的评估结果为true? [英] Why do empty JavaScript arrays evaluate to true in conditional structures?

问题描述

我在代码中遇到了很多错误，因为我期望这样的表达式:

I was encountering a lot of bugs in my code because I expected this expression:

Boolean([]); 评估为false.

但是情况并非如此，因为它评估为true.

But this wasn't the case as it evaluated to true.

因此，可能返回 [] 的函数是这样的:

Therefore, functions that possibly returned [] like this:

// Where myCollection possibly returned [ obj1, obj2, obj3] or []
if(myCollection)
{
  // ...

}else
{
  // ...
}

没有做预期的事情.

我误以为 [] 是一个空数组吗?

Am I mistaken in assuming that [] an empty array?

此外，此行为是否在所有浏览器中都一致?还是那里也有陷阱?顺便说一下，我在Goolgle Chrome中观察到了这种行为.

Also, Is this behavior consistent in all browsers? Or are there any gotchas there too? I observed this behavior in Goolgle Chrome by the way.

推荐答案

来自 http://www.sitepoint.com/javascript-truthy-falsy/

以下值始终是虚假的:

• false
• 0(零)
• "(空字符串)
• 空
• 未定义
• NaN (特殊的数字值，表示非数字！)

• false
• 0 (zero)
• "" (empty string)
• null
• undefined
• NaN (a special Number value meaning Not-a-Number!)

所有其他值都是真实的，包括"0"和"0".(引号为零)，"false"；(带引号的false)，空函数，空数组和空对象.

All other values are truthy, including "0" (zero in quotes), "false" (false in quotes), empty functions, empty arrays, and empty objects.

关于为什么是这样的，我怀疑这是因为JavaScript数组只是特定类型的对象.专门处理数组将需要额外的开销来测试 Array.isArray().此外，在这种情况下，如果真数组的行为与其他类似数组的对象不同，则可能会造成混淆，而使所​​有类似数组的对象的行为相同甚至会更加昂贵.

Regarding why this is so, I suspect it's because JavaScript arrays are just a particular type of object. Treating arrays specially would require extra overhead to test Array.isArray(). Also, it would probably be confusing if true arrays behaved differently from other array-like objects in this context, while making all array-like objects behave the same would be even more expensive.

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