Calculate the Tangent Line of a Circle

tangent.js

function tangentLine(M, r, alpha) {

   T = {
      x: M.x + Math.cos(alpha) * r,
      y: M.y + Math.sin(alpha) * r
   }

   v = {
      x: T.y - M.y,
      y: M.x - T.x
   }

   norm = Math.hypot(v.x, v.y)
   v.x/= norm
   v.y/= norm

   return [T, v]
}