How to use the base62.encode function in base62

function generateToken()
{
    return base62.encode(new Buffer(uuid.v4(null, [])).readUInt32LE(0));
} // end generateToken

test.serial('shorten url and retrieve its decoded value', async t => {
  const res = await urlService.shortenURL(testURL)
  t.is(res.url, testURL)
  t.is(res.base62, Base62.encode(res.numerical_id))

  const receivedURL = await urlService.getURL(res.base62)
  t.is(receivedURL.url, testURL)
  t.is(receivedURL.numerical_id, res.numerical_id)
})

export async function shortenURL(url) {
  if (!isURL(url)) {
    throw new Error('Invalid URL provided')
  }

  if (url.indexOf('//nazr.in') > -1) {
    throw new Error('URLs contain nazr.in can not to be shortened')
  }

  const shortLink = new ShortLink()
  await shortLink.save()
  shortLink.url = url
  shortLink.base62 = base64Encode(shortLink.numerical_id)
  await shortLink.save()
  return shortLink
}

function _generateAnonymousClassName(state) {
  var mungeNamespace = state.mungeNamespace || '';
  return '____Class' + mungeNamespace + base62.encode(_anonClassUUIDCounter++);
}

function _getMungedName(identName, state) {
  var mungeNamespace = state.mungeNamespace;
  var shouldMinify = state.g.opts.minify;

  if (shouldMinify) {
    if (!_mungedSymbolMaps[mungeNamespace]) {
      _mungedSymbolMaps[mungeNamespace] = {
        symbolMap: {},
        identUUIDCounter: 0
      };
    }

    var symbolMap = _mungedSymbolMaps[mungeNamespace].symbolMap;
    if (!symbolMap[identName]) {
      symbolMap[identName] =
        base62.encode(_mungedSymbolMaps[mungeNamespace].identUUIDCounter++);
    }
    identName = symbolMap[identName];
  }
  return '$' + mungeNamespace + identName;
}

function _generateAnonymousClassName(state) {
  var mungeNamespace = state.mungeNamespace || '';
  return '____Class' + mungeNamespace + base62.encode(_anonClassUUIDCounter++);
}

function _getMungedName(identName, state) {
  var mungeNamespace = state.mungeNamespace;
  var shouldMinify = state.g.opts.minify;

  if (shouldMinify) {
    if (!_mungedSymbolMaps[mungeNamespace]) {
      _mungedSymbolMaps[mungeNamespace] = {
        symbolMap: {},
        identUUIDCounter: 0
      };
    }

    var symbolMap = _mungedSymbolMaps[mungeNamespace].symbolMap;
    if (!symbolMap[identName]) {
      symbolMap[identName] =
        base62.encode(_mungedSymbolMaps[mungeNamespace].identUUIDCounter++);
    }
    identName = symbolMap[identName];
  }
  return '$' + mungeNamespace + identName;
}

function _getMungedName(identName, state) {
  var mungeNamespace = state.mungeNamespace;
  var shouldMinify = state.g.opts.minify;

  if (shouldMinify) {
    if (!_mungedSymbolMaps[mungeNamespace]) {
      _mungedSymbolMaps[mungeNamespace] = {
        symbolMap: {},
        identUUIDCounter: 0
      };
    }

    var symbolMap = _mungedSymbolMaps[mungeNamespace].symbolMap;
    if (!symbolMap[identName]) {
      symbolMap[identName] =
        base62.encode(_mungedSymbolMaps[mungeNamespace].identUUIDCounter++);
    }
    identName = symbolMap[identName];
  }
  return '$' + mungeNamespace + identName;
}

function _generateAnonymousClassName(state) {
  var mungeNamespace = state.mungeNamespace || '';
  return '____Class' + mungeNamespace + base62.encode(_anonClassUUIDCounter++);
}