Could you point me what babel do if there are no configuration, no .babel.config.js ?

babel src -d dist

It looks like it just regenerates the same code with new indenting, but I had noticed that it also removes function parameters trailing commas (ES8):

was:

function hi(a, b, ) {
  console.log(`hi ${a} and ${b}`);
}

become

function hi(a, b) {
  console.log(`hi ${a} and ${b}`);
}

What transformations "by default" also should be expected ? P.S. It is important to understand analyzing "non empty" configurations...