Math.random() 是如何工作的？

Question

So here we get a random number between 0 and 1 and round it down, so it always equals 0 right?

var random = Math.floor(Math.random());

And then here we times it by 5. So surely 0 * 5 will always equal to 0?

var random = Math.floor(Math.random() * 5);

So how does it return a number between 1 and 5?

Thanks

Answer 1

The expression

Math.floor(Math.random() * 5)

is evaluated by first calling Math.random() and then multiplying that result by 5. That will be a number between 0 and 5 (possibly equal to zero, but always less than 5).

Only then will that result be passed to Math.floor() .

Parenthesized subexpressions are evaluated first, in general. In this case, it's a function call, but that's still a good "rule of thumb" to keep in mind. "Work from the inside out", which is kind-of backwards from how you're supposed to use silverware at a fancy dinner. I confess to never having figured out what to do with the utensils at the top of the plate however.

Answer 2

Math.floor(Math.random() * 5)

.random() 生成 0 到 1 之间的随机数，.floor() 将数字向下舍入到最接近的整数。

Answer 3

var random = Math.round(Math.random() / (1/5))

这将使您的号码介于 1-5 之间。