Another option would be to use Array.some (if available) in the following way:
Array.prototype.contains = function(obj) {
return this.some( function(e){ return e === obj } );
}
The anonymous function passed to Array.some will return true if and only if there is an element in the array that is identical to obj. Absent such an element, the function will not return true for any of the elements of the array, so Array.some will return false as well.
