After checking on the w3c official website, I found that x-=y is equivalent to x = x-y; not x = y - x
x-=y is equivalent to x = x-y, established!
It is indeed my problem...
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
x-=y is equivalent to x = x-y, established!
It is indeed my problem...