how to create a transaction that can only run in bch-abc using javascript?
They added it to their examples.md recently.

var privateKey = new bch.PrivateKey('L1uyy5qTuGrVXrmrsvHWHgVzW9kKdrp27wBC7Vs6nZDTF2BRUVwy');
var utxo = {
  "txId" : "115e8f72f39fad874cfab0deed11a80f24f967a84079fb56ddf53ea02e308986",
  "outputIndex" : 0,
  "address" : "17XBj6iFEsf8kzDMGQk5ghZipxX49VXuaV",
  "script" : "76a91447862fe165e6121af80d5dde1ecb478ed170565b88ac",
  "satoshis" : 50000
};

var transaction = new bch.Transaction()
    .from(utxo)
    .addData('bch rocks') // Add OP_RETURN data
    .sign(privateKey);