OP_RETURN using Bitcore

OP_RETURN.js

// Extend the TransactionBuilder class to include OP_RETURN scripts.
// The two parameters are the amount to use for the output and the data
// to push onto the blockchain.
// This is done inside bitcore/lib/TransactionBuilder.js
TransactionBuilder.prototype.setUnspendableOutput = function(amount, msg) {
  var valueOutSat = bignum(0);
  var txobj = {};
  txobj.version = 1;
  txobj.lock_time = this.lockTime || 0;
  txobj.ins = [];
  txobj.outs = [];

  var amountSat = util.parseValue(amount);
  var value = util.bigIntToValue(amountSat);
  var data = msg || 0;
  var humanScript = "OP_RETURN " + data;
  var script = Script.fromHumanReadable(humanScript);
  var txout = {
    v: value,
    s: script.getBuffer(),
  };
  txobj.outs.push(txout);

  valueOutSat = valueOutSat.add(amountSat);

  this.valueOutSat = valueOutSat;

  this._setFeeAndRemainder(txobj);

  this.tx = new Transaction(txobj);
  return this;
};

// Usage is as follows:
function CreateOpReturnTx() {
        var opts = {
          // options
        };

        var utxos = [
          // unspent tx outputs
        ];

        var priv = [
          // private keys for utxos
        ];

        try {
          // Create the TX
          var TX = new Builder(opts)
            .setUnspent(utxos)
            .setUnspendableOutput(amount, 0x1234);
            .sign(priv)
            .build();
        }
        catch (err) {
          console.err(err.message);
        }
}