flyweight.js

var MyImmutableArray = (function() {
  var flyweight = {};
 
  return function(from, to) {
    var k = from + ':' + to;
    
    if (!flyweight[k]) {
      var array = [];
      for (var i = from; i <= to; i++) {
        array.push(i);
      }
      flyweight[k] = array;
    }
    return flyweight[k];
  };
})();

MyImmutableArray.prototype = Array.prototype;


console.log(new MyImmutableArray(1, 10000));
console.log(new MyImmutableArray(1, 10000));