为什么空的 JavaScript 数组在条件结构中评估为真? [英] Why do empty JavaScript arrays evaluate to true in conditional structures?

问题描述

我在我的代码中遇到了很多错误，因为我期望这个表达式:

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

Boolean([]); 求值为假.

但事实并非如此，因为它的评估结果为真.

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

因此，可能像这样返回 [] 的函数:

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.

我是否错误地假设 [] 是一个空数组?

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

此外，这种行为在所有浏览器中都一致吗?或者那里也有什么问题?顺便说一下，我在 Google 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/

以下值始终为假:

• 假
• 0(零)
• ""(空字符串)
• 空
• 未定义
• NaN(一个特殊的数值，表示非数字！)

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

所有其他值都是真值，包括 "0"(引号中为零)、"false"(引号中为 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 ({}).

关于为什么会这样，我怀疑这是因为 JavaScript 数组只是一种特定类型的对象.特殊处理数组需要额外的开销来测试 Array.isArray().此外，如果真正的数组在此上下文中的行为与其他类似数组的对象不同，这可能会令人困惑，而让所有类似数组的对象行为相同会更加昂贵.

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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