計算いろいろ。

calc.js

/**
 * calc - Some calculation utilities
 *
 * Copyright 2014 Yu Inao under the terms of the Unlicense
 * license found at http://unlicense.org/
 */
(function (root, factory) {
  /* global define, exports, require */
  'use strict';

  // AMD
  if ('function' === typeof define && define.amd) {
    define(['exports'], factory);

  // CommonJS
  } else if ('object' === typeof exports) {
    factory(exports);

  // Global variables
  } else {
    factory((root.resize = {}));
  }
})(this, function (exports) {
  /* global Math */
  'use strict';

  var WIDTH = 0, HEIGHT = 1;

  function longer_side (w, h) {
    if (w < h) return HEIGHT;
    return WIDTH;
  }

  function side_length (w, h, length, side) {
    if (WIDTH === side) return h / w * length;
    if (HEIGHT === side) return w / h * length;
  }

  /**
   * Scale width and height by longer side
   */
  function sides_by_longer_side (w, h, length) {
    var side = longer_side(w, h);
    if (WIDTH === side) {
      return {
        width: length,
        height: side_length(w, h, length, side)
      };
    }
    if (HEIGHT === side) {
      return {
        width: side_length(w, h, length, side),
        height: length
      };
    }
  }
  exports.sides_by_longer_side = sides_by_longer_side;

  /**
   * Degrees to radians
   */
  function d2r (deg) { return deg * Math.PI / 180; }
  exports.r2d = r2d;

  /**
   * Radians to degrees
   */
  function r2d (rad) { return rad * 180 / Math.PI; }
  exports.d2r = d2r;

});