Array.prototype.unique = function() {
    var uniqueKeys = {};
    var items = this.length;
    while ( items ) {
        uniqueKeys[ this[ --items ] ] = true;
    }

    var uniqueArray = [];
    for ( var key in uniqueKeys ) {
        if ( uniqueKeys.hasOwnProperty( key ) ) {
            continue;
        }
        uniqueArray.push( key );
    }

    return uniqueArray;
}