var names = [];
var namesLen = names.length;
for (i=0; i<namesLen; i++) {
    for (x=0; x<namesLen; x++) {
        if (names[i] === names[x] && (i !== x)) {alert('dupe')}
    }
}

function findDups(list) {
    var uniques = {}, val;
    var dups = {};
    for (var i = 0, len = list.length; i < len; i++) {
        val = list[i];
        if (val in uniques) {
            uniques[val]++;
            dups[val] = uniques[val];
        } else {
            uniques[val] = 1;
        }
    }
    return(dups);
}

var data = [1,2,3,4,5,2,3,2,6,8,9,9];
findDups(data);   // returns  {2: 3, 3: 2, 9: 2}

var data2 = [1,2,3,4,5,6,7,8,9];
findDups(data2);  // returns {}

var data3 = [1,1,1,1,1,2,3,4];
findDups(data3);  // returns {1: 5}

has_duplicates= A.some(function(itm){
    return A.indexOf(itm)===A.lastIndexOf(itm);
});

var list=new Array("foo", "bar", "foobar", "foo", "bar");
var newlist= new Array();
for(i in list){
    if(newlist[list[i]])
        newlist[list[i]]++;
    else
        newlist[list[i]]=1;
}