[рони]

tvv90,

function fn(a) {
    a = a.slice().sort(function(a, b) {
        return a - b
    });
    return a[a.indexOf(Math.max.apply(null, a))-1]
};
 alert( fn([-1, -2, -5, -25, -125]) );  //-2
 alert( fn([1, 1, 5, 5]) );  //1
 alert( fn([1, 2, 3, 4, 5, 5]) );  //4