IN Operator in Javascript functions like the one in SQL

I have tried the following but it's throwing an exception:

                if (!$get('sslot_hf0').value in ('X', 'Y', 'Z', '0')) {
                $get('sslot_hf0').value = 'X';
            }

I am looking for a function similar to the IN operator in SQL

You can use below function for the same purpose, second param can be array or object and first param is value you are searching in array or object.

   function inStruct(val,structure)
        {

          for(a in structure)
             {
               if(structure[a] == val)
                 {
                   return true;
                 }
             }
           return false;
        }
if(inStruct('Z',['A','B','Z']))
    {
       //do your stuff
    }

// this function traverse through inherited properties also

i.e in some where your included js libraries

Array.prototype.foo = 10;

than

 instruct(10,[1,2,3]) // will return true

same will happen for objects also. check this fiddle http://jsfiddle.net/rQ8AH/17/

EDITED ::

thank you all for comments ... this is the updated code, I thought it is better to keep old function also. so, some one can notice the difference.

function inStruct(val,structure)
    {

      for(a in structure)
         {

           if(structure[a] == val && structure.hasOwnProperty(a))
             {
               return true;
             }
         }
       return false;
    }