如何（false == false == true）为真

Question

While I was programming I had an unexpected outcome in my if statement.

How in the world can this code alert true? I didn't found anything that could help me at W3S, and really would like to know why these alerts "true"

window.alert(false == false == true); //alerts true
window.alert(false == (false == true));//even this alerts true

Answer 1

First Case

false == false == true

will be evaluated as

(false == false) == true

because expressions are evaluated from left to right , by default. which reduces to

true == true

since false is actually equal to false . That is why it is evaluated to true .

Second Case

false == (false == true)

is reduced to

false == false

because false is not equal to true . That is why the entire expression is true because false is equal to false .

Answer 2

The execution will start from left hand side.

window.alert(false == false == true); 

at first false== false is true. Then true==true is true.

In second case, since you have using parenthesis () that will be executed at first.

false == true is false.

Then false == false is true.

Answer 3

Is it true that false == true ? I think it is apparent that this is not true, thus (false == true) is false and therefor false == (false == true) (as we've already noticed that the second part is false).

As for the first example - actually no matter the order of evaluation it will hold true(I leave that to you as a logical exercise). Still javascript guarantees the evaluation order to be left to right thus this expression is the same as (false == false) == true . Again I leave to you to prove this is true.

Answer 4

 false == false == true 

false == false , this is true , which equals true .

 false == (false == true) 

false == true , this is false , which equals false .

Answer 5

First line - from left to right it compares false == false which is true , then compared to true returns true

Second line - from left to right it compares (false == true) which is false , then comparison of false and false returns true

Answer 6

Both are correct.

Case 1: false == false == true
this is similar to (false == false) == true

The evaluation is false == false IS true and true == true IS true

Case 2: false == (false == true)
this is similar to (false == true) == false

The evaluation is false == true IS false and false == false IS true

Hope this helps