But because it lacks a var declaration, it's a global variable.

但它缺少var声明，这是个全局变量。

youdao

Incrementing a global variable is 2 times slow than a local var.

递增一个全局变量要比递增一个局部变量慢2倍。

youdao

Just declaring a global variable without using it in a function also slows things down (by about the same amount as incrementing a local var).

仅定义一个局部变量而没在函数中调用它，同样会减慢速度(其程度相当于递增一个局部变量)。

youdao