JavaScript中布尔值的数学运算符

Question

Can someone explain what will be the order of execution of following JavaScript Code:

(true + false) > 2 + true

I understand using + operator over two Boolean values returns the result as 0,1 or 2 depending upon the values being provided.

I interpreted output of above code as 1 by breaking the execution in following order:

1) (true + false) // Outputs : 1
2) 1 > 2 // Outputs : false
3) false + true //Outputs : 1

But the actual result is:

false

Can anyone correct my understanding if am interpreting the code in wrong way.

Answer 1

Your 2nd point is not correct.

1) (true + false) outputs - 1
2) (2 + true) - outputs 3
3) 1 > 3 - outputs false

You can check this using functions

 (true + false) > 2 + true function f1() { const cond = true + false; console.log(cond); return cond; } function f2() { const cond = 2 + true; console.log(cond); return cond; } console.log(f1() > f2()); 

If you want to compare with 2 then add true, you must to wrap into the parentheses

((true + false) > 2) + true

Answer 2

What you have is a question of operator precedence , of three parts,

• ( ... ) grouping with the highest precedence of 20,

• + adition with precedence of 13, and

• > greater than (here) with the lowest precendece of 11.

That means the operators with higer precedence are evaluated first and the comes the once with lower precedence.

(true + false) > 2 + true
(true + false)             -> 1
                 2 + true  -> 3

             1 > 3         -> false