src/language-js/print/member.js/printMemberLookup
function printMemberLookup(path, options, print) {
  const property = path.call(print, "property");
  const n = path.getValue();
  const optional = printOptionalToken(path);

  if (!n.computed) {
    return concat([optional, ".", property]);
  }

  if (!n.property || isNumericLiteral(n.property)) {
    return concat([optional, "[", property, "]"]);
  }

  return group(
    concat([optional, "[", indent(concat([softline, property])), softline, "]"])
  );
}