left-pad vs array vs log(n)

<script>

/*
padString1 finished in 652 ms
padString2 finished in 2619 ms
padString3 finished in 17 ms
*/

function padString1(str, len, ch) {
  var len = len - str.length;
  var i = -1;
  while (++i < len) {
    str = ch + str;
  }
  return str;
}

function padString2(str, len, ch) {
  return Array(len + 1 - str.length).join(ch) + str;
}


function padString3 (str, len, ch) {
  str = String(str);

  if (!ch && ch !== 0) ch = ' ';

  len = len - str.length;
  if (len <= 0) return str;

  ch = ch + '';
  var pad = '';
  while (true) {
    if (len & 1) pad += ch;
    len >>= 1;
    if (len) ch += ch;
    else break;
  }
  return pad + str;
}

var timer = function(name) {
    var start = new Date();
    return {
        stop: function() {
            var end  = new Date();
            var time = end.getTime() - start.getTime();
            console.log('Timer:', name, 'finished in', time, 'ms');
        }
    }
};

var padIter = 50000;
var padLen = 1000;

var t = timer('padString1');

for (var i=0; i<padIter; i++) {
    var str = padString1("hello world", padLen, " ");
//  console.log(str);
}

t.stop();

var t = timer('padString2');

for (var i=0; i<padIter; i++) {
    var str = padString2("hello world", padLen, " ");
//  console.log(str);
}

t.stop();

var t = timer('padString3');

for (var i=0; i<padIter; i++) {
    var str = padString3("hello world", padLen, " ");
//  console.log(str);
}

t.stop();

</script>