“value == var”与“var == value”相对 [英] "value == var" versus "var == value"

问题描述

在很多地方，我看到开发人员正在进行 value == var 比较，如下所示：

At many places, I've seen developers doing value == var comparisons, like this:

if ('https' === location.protocol) {
   port = 8443;
   protocol = 'wss://';
   isSecure = true;
}

我知道 a == b 与 b == a 相同，那么为什么人们使用 value == var 而不是 var == value ？

I know that a == b is same as b == a, so why do people use value == var instead of var == value?

这是否有标准？如果是，那是标准方式？

Is there a standard for this? And if yes, which is the standard way?

推荐答案

您所看到的是 yoda条件。

尤达条件描述的是相同的表达式，但是相反：

Yoda conditions describe the same expression, but reversed:

if ( 42 == $value ) { /* ... */ }
// Reads like: "If 42 equals the value..."

优点是

在表达式中放置常量值不会改变程序的行为（除非值计算为false - 见下文）。在使用单个等号（=）进行赋值而不进行比较的编程语言中，可能的错误是无意中分配值而不是编写条件语句。

Placing the constant value in the expression does not change the behavior of the program (unless the values evaluate to false—see below). In programming languages that use a single equals sign (=) for assignment and not for comparison, a possible mistake is to assign a value unintentionally instead of writing a conditional statement.

请注意，它显然缺乏可读性。我个人不喜欢这种方式。

Note that it is clearly lack of readability. I personally don't prefer this way.

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