JavaScript的双等于（==）总是对称的吗？ [英] Is JavaScript's double equals (==) always symmetric?

问题描述

在许多情况下，JavaScript的类型强制相等运算符不可传递。例如，请参阅 JavaScript等同传递性很奇怪。

There are many cases in which JavaScript's type-coercing equality operator is not transitive. For example, see "JavaScript equality transitivity is weird."

但是，有没有 == 不是对称的情况？也就是说， a == b 是 true 和 b == a 是 false ？

However, are there any cases in which == isn't symmetric? That is, where a == b is true and b == a is false?

推荐答案

在Javascript中， == 始终对称。

In Javascript, == is always symmetric.

规范说：

注2：等于运算符
维护以下不变量：

NOTE 2 The equality operators maintain the following invariants:

• A！= B 相当于！（A == B）。


• A == B 相当于 B == A ，除了评估
  的顺序 A和B 。

• A != B is equivalent to !(A == B).
• A == B is equivalent to B == A, except in the order of evaluation of A and B.

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