How to use the format.padLeft function in format

exports.createDCFFilename = function(storage, type, callback) {

  // We havent loaded the current counters from indexedDB yet, defer
  // the call
  if (!dcfConfigLoaded) {
    deferredArgs = {storage: storage, type: type, callback: callback};
    return;
  }

  var dir = 'DCIM/' + dcfConfig.seq.dir + dcfConfig.postFix + '/';
  var filename = dcfConfig.prefix[type] +
    format.padLeft(dcfConfig.seq.file, 4, '0') + '.' +
    dcfConfig.ext[type];
  var filepath = dir + filename;

  // A file with this name may have been written by the user or
  // our indexeddb sequence tracker was cleared, check we wont overwrite
  // anything
  var req = storage.get(filepath);

  // A file existed, we bump the directory then try to generate a
  // new filename
  req.onsuccess = function() {
    dcfConfig.seq.file = 1;
    dcfConfig.seq.dir += 1;
    asyncStorage.setItem(dcfConfig.key, dcfConfig.seq, function() {
      exports.createDCFFilename(storage, type, callback);
    });

exports.createDCFFilename = function(storage, type, callback) {

  // We havent loaded the current counters from indexedDB yet, defer
  // the call
  if (!dcfConfigLoaded) {
    deferredArgs = {storage: storage, type: type, callback: callback};
    return;
  }

  var dir = 'DCIM/' + dcfConfig.seq.dir + dcfConfig.postFix + '/';
  var filename = dcfConfig.prefix[type] +
    format.padLeft(dcfConfig.seq.file, 4, '0') + '.' +
    dcfConfig.ext[type];
  var filepath = dir + filename;

  // A file with this name may have been written by the user or
  // our indexeddb sequence tracker was cleared, check we wont overwrite
  // anything
  var req = storage.get(filepath);

  // A file existed, we bump the directory then try to generate a
  // new filename
  req.onsuccess = function() {
    dcfConfig.seq.file = 1;
    dcfConfig.seq.dir += 1;
    asyncStorage.setItem(dcfConfig.key, dcfConfig.seq, function() {
      exports.createDCFFilename(storage, type, callback);
    });

function digits(value) {
  return format.padLeft(value, 2, '0');
}