subarray.js

var makeSubArray = (function(){

  var MAX_SIGNED_INT_VALUE = Math.pow(2, 32) - 1,
      hasOwnProperty = Object.prototype.hasOwnProperty;

  function ToUint32(value) {
    return value >>> 0;
  }

  function getMaxIndexProperty(object) {
    var maxIndex = -1, isValidProperty;
    
    for (var prop in object) {
      
      isValidProperty = (
        String(ToUint32(prop)) === prop && 
        ToUint32(prop) !== MAX_SIGNED_INT_VALUE && 
        hasOwnProperty.call(object, prop));
        
      if (isValidProperty && prop > maxIndex) {
        maxIndex = prop;
      }
    }
    return maxIndex;
  }

  return function(methods) {
    var length = 0;
    methods = methods || { };

    methods.length = {
      get: function() {
        var maxIndexProperty = +getMaxIndexProperty(this);
        return Math.max(length, maxIndexProperty + 1);
      },
      set: function(value) {
        var constrainedValue = ToUint32(value);
        if (constrainedValue !== +value) {
          throw new RangeError();
        }
        for (var i = constrainedValue, len = this.length; i < len; i++) {
          delete this[i];
        }
        length = constrainedValue;
      }
    };
    methods.toString = {
      value: Array.prototype.join
    };
    return Object.create(Array.prototype, methods);
  };
})();

function SubArray() {
  var arr = makeSubArray();
  if (arguments.length === 1) {
    arr.length = arguments[0];
  }
  else {
    arr.push.apply(arr, arguments);
  }
  return arr;
}