Modify floor/ceiling function to work with numbers other than 1?

Question

By default the floor function always rounds down and the ceil function always rounds up to the nearest '1'

How would I round down/up to the nearest 20, or the nearest 1,000?

Say I had a number x and a factor y.

I want to find the closest factor of y to x.

I am using this to find maximum and minimum values for a graph. Thanks.

Answer 1

简单：

var z = y * Math.floor(x / y);

Answer 2

Math.floor(x / 20) * 20;
Math.ceil(x / 20) * 20;

In your case:

Math.floor(x / y) * y;

The x / y turns the expression into units of y ; with .floor() or .ceil() you then round it down or up; afterwards you multiply with y again to get your final answer.