How to get notified when an event triggers on ethereum smart contract?

0 votes

When someone makes a transfer from my account, an event gets trigger name

event Transfer(address indexed from, address indexed to, uint to)

Now I want to get notified when this event occurs on smart contract. I tried different things like filter, watch, subscription and etc. But nothing works as per need.

I also have another query What does filter, subscribe, and watch exactly do. I am always getting confused between these terms. Can someone give a clear idea?

Jun 8, 2018 in Blockchain by charlie_brown
• 7,710 points

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0 votes

Here's a simple example for web3js 1.0.0.beta*:

function handler (event) {

function errorCallback (err) {

let subscription =;
subscription.on('data', handler).on('error', errorCallback);

To unsubscribe:

subscription.unsubscribe(function (result) {

Example of usage in class:

class Listener {
  constructor(event, handler) {
    this.subscription = event;
    this.subscription.on('data', handler).on('error', this.errorCallback);

  errorCallback(err) {

class Test {
  constructor(contractObj) {
    this.contractObj = contractObj;

  createListener() {
    let self = this;
    this.listener = new Listener(, function (event) {
      self.returnValues = event.returnValues;
answered Jun 8, 2018 by ariaholic
• 7,320 points

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