LazyArray.js - A JavaScript LazyArray implementation

LazyArray.js exposes an 'extend' method, which accepts an object
containing methods and properties to apply to the new function
it returns. The only required property is a 'load' method, which
should return an array.

The load function you provided will automatically be called when
an iterator function is called. The following functions are
wrapped to call your load function: filter, forEach, every, map,
some, reduce, and reduceRight.

Usage:

  var Query = LazyArray.extend({
    load: function() {
      return [1, 2, 3, 4, 5, 6, 7, 8];
    }
  });

  var query = new Query();
  query.loaded // => false
  query.length // => 0
  query.filter(function(v) { return v % 2 == 0 }) // => [2, 4, 6, 8]
  query.loaded // => true
  query.length // => 8