BEGIN {
  require JSON;
  JSON->import(qw(encode_json decode_json));
}
##</code><code>##

  # Note that JSON version 2.0 and above will automatically use JSON::XS
  # if available, at virtually no speed overhead either, so you should
  # be able to just:

  use JSON;

  # and do the same things, except that you have a pure-perl fallback now.