Testing which Reverse String methods are faster... run it here: http://jsperf.com/reverse-speeds/2

ReverseSpeeds.js

// Run tests
function run_test(func) {
  var j, s = 'asdfasdfasdf', name = func.name;
  
  console.time(name);
  for(j = 0; j <= 10000; j++) {
    func(s);
  }
  console.timeEnd(name);
}

// split join reverse
function reverse_split_join(s) {
  return s.split('').reverse().join('');
}

// For Negative Concat
function reverse_for_neg_concat(s) {
  var reverse = '';
  for(i = s.length-1; i >= 0; i--) {
    reverse += s[i];
  }
  return reverse;
}

// For Negative join
function reverse_for_neg_join(s) {
  var reverse = [];
  for(i = s.length-1; i >= 0; i--) {
    reverse.push(s[i]);
  }
  return reverse.join('');
}

// For Positive Concat
function reverse_for_pos_concat(s) {
  var reverse = '', _ref = s.length - 1;
  for(i = 0; i <= _ref; i++) {
    reverse += value[_ref - i];
  }
  return reverse;
}

// For Positive Join
function reverse_for_pos_join(s) {
  var reverse = [], _ref = s.length - 1;
  for(i = 0; i <= _ref; i++) {
    reverse.push(value[_ref - i]);
  }
  return reverse;
}

// While Negative Concat
function reverse_while_neg_concat(s) {
  var reverse = '', _ref = s.length-1;
  i = _ref;
  while(i >= 0) {
    reverse += s[i];
    i--;
  }
  return reverse;
}

// While Negative Join
function reverse_while_neg_join(s) {
  var reverse = [], _ref = s.length-1;
  i = _ref;
  while(i >= 0) {
    reverse.push(s[i]);
    i--;
  }
  return reverse.join('');
}

// While Positive Concat
function reverse_while_pos_concat(s) {
  var reverse = [], i = 0;
  while(i <= s.length-1) {
    reverse += s[i];
    i++;
  }
  return reverse;
}

// While Positive Join
function reverse_while_pos_join(s) {
  var reverse = [], i = 0;
  while(i <= s.length-1) {
    reverse.push(s[i]);
    i++;
  }
  return reverse.join('');
}

run_test(reverse_split_join);
run_test(reverse_for_neg_concat);
run_test(reverse_for_neg_join);
run_test(reverse_for_pos_concat);
run_test(reverse_for_pos_join);
run_test(reverse_while_neg_concat);
run_test(reverse_while_neg_join);
run_test(reverse_while_pos_concat);
run_test(reverse_while_pos_join);