Javascript缩小比较语句 [英] Javascript minification of comparison statements

问题描述

我正在查看由闭包生成的一个缩小的js文件。我发现无论我在哪里检查变量和字符串之间是否相等，

I was looking over one of the minified js files generated by closure. I found that wherever I'm checking for equality between a variable and string like,

a == "13" || a == "40"

闭包替换为

"13" == a || "40" == a

为什么要进行此修改？这里有一些性能优势吗？

Why is this modification done? Is there some performance advantage here?

推荐答案

[更新：请参阅@ John的回答，这对于为什么更有意义一个js minifier会这样做，应该是接受的答案]

作为一般概念，这是为了避免程序员错误。如果您手动修改代码并将变量放在第一位且常数为第二位，则可能会意外输入：

As a general concept, this is to avoid programmer error. If you were modifying the code manually and put the variable first and constant second, it's possible to accidentally type:

a == '40' || a = '13'

哎呀！我们只需将 a 设置为 '13'而不是比较。通过将常数放在左边，我们避免了这种可能性：

Oops! We just set a to '13' instead of comparing. By putting the constant on the left, we avoid this possibility:

'40' == a || '13' = a

因为你不能在左边放一个常量字符串会引发异常分配操作之手。

Will throw an exception because you can't put a constant string on the left hand of an assignment operation.

所以在某些思想流派中，最好的做法是在与常量进行相等比较时始终将常量放在左边。看起来像关闭遵循这种做法。

So in some schools of thought, it's best practice to always put the constant on the left when doing equality comparison against a constant. Looks like closure follows that practice.

这些被称为yoda条件。

These are called "yoda conditions".

请注意我的个人偏好在大多数情况下实际上只是将常量放在右边，因为代码往往更好地读取，所以我认为权衡不够好。但我看到了尤达条件背后的逻辑。

Note that my personal preference is to actually to just put the constant on the right in most cases, because the code tends to read better, so I don't think the tradeoff is good enough. But I see the logic behind yoda conditions.

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