Angle type

angle.js

function Angle(radians) {
  this._radians = radians;
}

Angle.prototype = {
  degrees: function(degrees) {
  	this._radians = degrees / 180 * Math.PI;
  	return this;
  },
  radians: function(radians) {
  	this._radians = radians;
  	return this;
  },
  
  asDegrees: function() {
  	return this._radians / Math.PI * 180;
  },
  asRadians: function() {
  	return this._radians;
  },
  
  add: function(angle) {
  	this._radians += angle;
  	return this;
  },
  multiply: function(factor) {
    this._radians *= factor;
  	return this;
  },
  
  valueOf: function() {
  	return this._radians;
  }
};

Usage

var a = new Angle().radians(Math.PI * 3 / 4), 
    b = new Angle().degrees(135);

var c = new Angle(a + b);

Math.sin(a);
Math.cos(b);

a.add(new Angle().degrees(30));
b.add(Math.PI);

c.multiply(1.5);

nice
toDegrees and toRadians i would say

parse strings:
var a = new Angle().fromString('90deg'); or var b = AngleFromString('90deg');

a.add(b) // PI

+1 new Angle().fromString('90deg');