[рони]

На всякий случай

reverse()

= return b-a;

var array = [1, 2, 1, 10, 5, 3, 4, 40, 50], i = array.length, result = [];

array.sort(function(a,b) {
*!*
    return b-a;
*/!*
});

while(i--){
    if(result.join().search(array[i]+'\\b') == '-1') {
        result.push(array[i]);
    }
}

alert(result);