JavaScript三等于和三变量比较

Question

有人可以解释这个吗？

1 == 1  //true, as expected 
1 === 1  //true, as expected 
1 == 1 == 1 //true, as expected 
1 == 1 == 2 //false, as expected 
1 === 1 === 2 //false, as expected 
1 === 1 === 1 //false? <-- 

也有布尔逻辑，超过两个号码以这种方式进行比较的名称（我把它叫做“三变的比较”，但我认为这会是错误的...）

Answer 1

该表达式：

1 === 1 === 1 

被评价为：

(1 === 1) === 1 

评估圆括号内的表达式后：

true === 1 

并且该表达式在逻辑上是错误的。下面的表达式返回true如同预期：

1 === 1 === true 

Answer 2

平等是一个left-to-right precedence operation。

所以：

1 == 1 == 1 
true == 1 
true 

和：

1 === 1 === 1 
true === 1 
false // because triple-equals checks type as well