leftpad.js

function leftpad(content, length, pad){
  // make sure this is a proper string
  content = String(content);
  // get the pad character if set (or if zero)
  pad = String(pad || pad === 0 ? pad : '')[0];
  // get the extra length we need to add, but not less than zero if it's already longer
  var left = Math.max(length-content.length, 0);
  // voila!
  return pad.repeat(left) + content;
}