Select a random letter from A to Z based on letter frequency in the English language

randomAtoZ.js

  var randomAtoZ = (function (lookup) {
    return function () {
      var random = Math.random() * 100000,
          letter;
      for (letter in lookup) {
        if (random < lookup[letter]) {
          return letter;
        }
      }
    }
  })({
    // Ranges calculated from data found at
    // http://en.wikipedia.org/wiki/Letter_frequency
    a: 8167,  b: 9659,  c: 12441, d: 16694,
    e: 29396, f: 31624, g: 33639, h: 39733,
    i: 46699, j: 46852, k: 47624, l: 51649,
    m: 54055, n: 60804, o: 68311, p: 70240,
    q: 70335, r: 76322, s: 82649, t: 91705,
    u: 94463, v: 95441, w: 97801, x: 97951,
    y: 99925, z: 100000
  });