var arr = [ "a", "b", "c", "d", "e" ]
$("div").text(arr.join(", "));
arr = jQuery.map(arr, function(n, i){
return (n.toUpperCase() + i);
});
$("p").text(arr.join(", "));
arr = jQuery.map(arr, function (n, i) {
var x = n + n;
if (i==1) return null;
if (i==3) return [x, x, x];
return x;
});
$("span").text(arr.join(", "));