grid_space.js

// think of this as the "constructor" function - returns a GridSpace object
// so do your init stuff here
var GridSpace = function (x, y, height) {
  this.x = x;
  this.y = y;
  this.height = height;
};

// this of this as sort of the "class definition", define your other functions here
// be warned though: everything in the prototype is shared between all GridSpace instances!
GridSpace.prototype = {
  /** 
   * ...so don't do this in the prototype...
   *
   * x: null,
   * y: null,
   *
   * ...becuase then every GridSpace instance would have the same x and y
   */
  compareTo: function (height) {
    if (this.height > height) return 1;
    if (this.height < height) return -1;
    return 0;
  }
};

// need to expose if in a Node.js environment
if (typeof exports != 'undefined') exports.GridSpace = GridSpace;

gs_test.js

var assert = require('assert');

describe('GridSpace', function () {
  var GridSpace = require('../grid_space.js').GridSpace;
  
  describe('#compareTo(height)', function () {
    it('should return -1 when this.height is smaller than height', function () {
      // setup
      var gs = new GridSpace(1, 2, 5);

      // exercise/verify
      assert.equal(-1, gs.compareTo(6);
    });
  });
});