问题描述

我正在阅读关于 JavaScript 的 Mozilla 手册，我在阅读中来到了这一点，布尔对象.我看不到它们的单一用途.他们的意义何在?为什么不只使用 true 和 false?

I am reading through the Mozilla Manual on JavaScript, and I come to this point in my reading, Boolean object. I can't see a single use for them. What's their point? Why wouldn't you use just true and false?

顺便说一句，我根本不懂 Java，而且我不害怕学习新事物，这也是我尝试学习 JavaScript 的原因.我是一名 PHP 程序员，一名后端人员，我想学习如何做一些前端工作，所以我正在阅读 Mozilla JavaScript 指南.

By the way, I don't know Java at all and I'm not afraid of learning new things that consequently why I'm trying to learn JavaScript. I'm a PHP programmer, a back end guy, and I'd like to learn how to do some front end work, so I'm reading the Mozilla JavaScript Guide.

推荐答案

因为这是(有点遗憾)语言的定义方式——我怀疑它最初是为了性能/优化；请注意下面分配给 string 属性的情况.(Java 的工作方式类似，尽管 Scala 和 Python 在很大程度上拒绝这种区别).

Because this is (somewhat sadly) how the language was defined -- I suspect it was originally for performance/optimization; note the case of assignment to a string property below. (Java works similarly, although Scala and Python largely reject this distinction).

请注意，Boolean 并不是唯一的包装器类型".例如，还有 String 和 Number.

Note that Boolean isn't the only "wrapper type". There are also String and Number, for instance.

因此，仍然存在许多怪癖(以下可能同样适用于布尔值):

Because of this there remains a number of quirks (the below could just as much apply to Boolean):

typeof("foo") // string
typeof(new String("foo")) // object
"foo" instanceof String // false
new String("foo") instanceof String // true

// result is undefined: a string is a primitive and silently "ate" the assignment
// this also makes it a much cheaper value as it's not a "real" object
x = "f"; x.bar = 42; x.bar

// result is 42: a String is a "real" object with real properties!
// however, this also means that it may have a good bit more overhead
x = new String("f"); x.bar = 42; x.bar

我知道这并没有回答"这个问题，而是在火上扔了一些木头；-)

I know this didn't "answer" the question, but rather chucks some more wood on the fire ;-)

上述唯一真正的陷阱"可能是 new Boolean(false) 是一个真值.

The only real "gotcha" otherwise from the above is that perhaps new Boolean(false) is a truth-y value.

编码愉快.

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