http://lawrence.ecorp.net/inet/sampl...exp-format.php

da cui estraggo

function padleft(val, ch, num) {
var re = new RegExp(".{" + num + "}$");
var pad = "";
if (!ch) ch = " ";
do {
pad += ch;
}while(pad.length < num);
return re.exec(pad + val);
}
function padright(val, ch, num){
var re = new RegExp("^.{" + num + "}");
var pad = "";
if (!ch) ch = " ";
do {
pad += ch;
} while (pad.length < num);
return re.exec(val + pad);
}