JavaScript
Blockchain
Ethereum
truffle

Truffle でイベントを監視する

ここを読みましょう。
Interacting with your contracts - Truffle

app.js
window.App = {
  start: function() {
    const self = this;

    // Catching events
    self.catchEvents();
    });
  },

  catchEvents: function() {
    MetaCoin.deployed().then(instance => {
      const transfers = instance.Transfer({fromBlock: 'latest'});
      transfers.watch((error, result) => {
        if (error == null) {
          console.log('Transfer:', result.args);
        }
      });
    }).catch(e => {
      console.log(e);
    });
  }
};

出力例

{
  from: "0xb2743d3f9d650b69624034a9b7c63a0151658d9b",
  to: "0x4cbca99431f5c26efa0d9bcbd35cb4db525ab8eb",
  value: BigNumber {s: 1, e: 2, c: Array(1)},
}