Duplicate in array check

Checks for duplicates in array and shows in alert box

by mattography

JavaScript

var array = [0,4,5,2,5,6,103,1,1,4,2,304];

array.sort();
var last = array[0];
for (var i=1; i<array.length; i++) {
   if (array[i] == last) alert('Duplicate : '+last);
   last = array[i];
}