subset_of.js

utils = {
  subset_of: function(arr) {
    for(var i = arr.length, d = {}; i--;) d[arr[i]] = 1;
    var p, before = 0, after = 0; 
    for(p in d) before++;
    for(i = this.length; i--;) d[this[i]] = 1;
    for(p in d) after++;
    return after == before;
  }
}

arr = [1,2];
arr.subset_of = utils.subset_of;
console.log(arr.subset_of([2,3,4])); // false
console.log(arr.subset_of([1,2,3,4])); // true

// #flashcodersfeelings

LOL