Check if every element in one array is in a second array

Do you have to support crummy browsers? If not, the every function should make this easy.

If arr1 is a superset of arr2, then each member in arr2 must be present in arr1

var isSuperset = arr2.every(function(val) { return arr1.indexOf(val) >= 0; });

Here’s a fiddle

EDIT

So you’re defining superset such that for each element in arr2, it occurs in arr1 the same number of times? I think filter will help you do that (grab the shim from the preceding MDN link to support older browsers):

var isSuperset = arr2.every(function (val) { 
    var numIn1 = arr1.filter(function(el) { return el === val;  }).length;
    var numIn2 = arr2.filter(function(el) { return el === val;  }).length;
    return numIn1 === numIn2;   
});

Updated Fiddle

END EDIT

---

If you do want to support older browsers, the MDN link above has a shim you can add, which I reproduce here for your convenience:

if (!Array.prototype.every)  
{  
  Array.prototype.every = function(fun /*, thisp */)  
  {  
    "use strict";  

    if (this == null)  
      throw new TypeError();  

    var t = Object(this);  
    var len = t.length >>> 0;  
    if (typeof fun != "function")  
      throw new TypeError();  

    var thisp = arguments[1];  
    for (var i = 0; i < len; i++)  
    {  
      if (i in t && !fun.call(thisp, t[i], i, t))  
        return false;  
    }  

    return true;  
  };  
}  

EDIT

Note that this will be an O(N²) algorithm, so avoid running it on large arrays.