triangles.js

// Something on the internet reminded me of triangles.

var _ = require("underscore");

//Some basic vector maths
var v = {
  add: function(u,v) {
    return _.zip(u,v).map(function(t) { return t[0]+t[1]; });
  },
  sub: function(u,v) {
    return _.zip(u,v).map(function(t) { return t[0]-t[1]; });
  },
  norm: function(u) {
    return Math.pow(u.reduce(function(acc, x) {
      return acc + Math.pow(x, 2);
      }, 0), 0.5); 
  }
};

// Three points representing the vertices of a triangle, then side lengths.
// A combinations function would increase the DRYness.
var a = [0, 0],
    b = a.map(function() { return Math.random(); }),
    c = a.map(function() { return Math.random(); }),
    ab = v.norm(v.sub(a,b)),
    ac = v.norm(v.sub(a,c)),
    bc = v.norm(v.sub(b,c));

// http://en.wikipedia.org/wiki/Area_of_triangle#Using_coordinates as it turns out

var area = (function (b,c) {
  return Math.abs(b[0]*c[1] - c[0]*b[1])/2;
})(v.sub(b,a), b.sub(c,a));