Javascript how to show each element of array on a new line

The for-loop is suspicious. Firstly, you do not process all items (the last one is missing, as @sarfraz pointed out). Sencondly you are returning the result (zzz) in the for-loop body:

for (var i=0; i<=xxx; i++)
{
  zzz[i] = zzz[i] + '<br />';
  return zzz; // for-loop will stop here! resulting in ["value1<br />", "Value2", etc...]
}

In Javscript you can simple "join" the array:

return dates.split(',').join("<br />")

Since you are simply replacing strings you could use the replace method:

return dates.replace(",", "<br />");

i have modified your function bit cleaner.since already stefan mentioned your mistake.

function splitDate(dates) {
    if (dates != null)
    {
        var dates = dates.split(',');
        var xxx = dates.length;
        console.log(xxx);
        for (var i=0; i<xxx; i++)
        {
            dates[i] = dates[i];                    
        }
    }
    console.log(dates.join('\r\n'));
    return dates.join('\r\n');        
}

the above function you can do it in a single line:

if it's an array you can split into new line in following way:

var arr = ['apple','banana','mango'];
console.log(arr.join('\r\n'));

if it's a string:

var str = "apple,banana,mango";
console.log(str.split(',').join("\r\n"));