Found an answer. The problem is that String.fromCharCode takes multiple arguments and Array.map also passes multiple arguments to the callback, therefore the e

Found an answer. The problem is that String.fromCharCode takes multiple arguments and Array.map also passes multiple arguments to the callback, therefore the equivalent of numbers.map(String.fromCharCode) is actually: numbers.map(function(x, y, z){return String.fromCharCode(x, y, z);}) Which of course is slower as the end result will actually be array with longer strings in it.