The cited answer was wrong. You had to change

csvContent += index < infoArray.length ? dataString+ n : dataString;

to

csvContent += dataString + n;

As to why the cited answer was wrong (funny it has been accepted!): index, the second parameter of the forEach callback function, is the index in the looped-upon array, and it makes no sense to compare this to the size of infoArray, which is an item of said array (which happens to be an array too).

EDIT

Six years have passed now since I wrote this answer. Many things have changed, including browsers. The following was part of the answer:

START of aged part

BTW, the cited code is suboptimal. You should avoid to repeatedly append to a string. You should append to an array instead, and do an array.join(n) at the end. Like this:

var lineArray = [];

data.forEach(function (infoArray, index) {

    var line = infoArray.join(,);

    lineArray.push(index == 0 ? data:text/csv;charset=utf-8, + line : line);

});

var csvContent = lineArray.join(n);

END of aged part

(Keep in mind that the CSV case is a bit different from generic string concatenation, since for every string you also have to add the separator.)

Anyway, the above seems not to be true anymore, at least not for Chrome and Firefox (it seems to still be true for Safari, though).

To put an end to uncertainty, I wrote a jsPerf test that tests whether, in order to concatenate strings in a comma-separated way, it's faster to push them onto an array and join the array, or to concatenate them first with the comma, and then directly with the result string using the += operator.

Please follow the link and run the test, so that we have enough data to be able to talk about facts instead of opinions.