You can use a function like this to do the conversion:

function toDegrees (angle) {
  return angle * (180 / Math.PI);

Note that functions like sin, cos, and so on do not return angles , they take angles as input. It seems to me that it would be more useful to you to have a function that converts a degree input to radians, like this:

function toRadians (angle) {
  return angle * (Math.PI / 180);

which you could use to do something like tan(toRadians(45)).