annot implement web3 eth subscribe on Web3 version 1 0 0-beta 27

Question

I am running a private ethereum blockchain on web3 version 1.0.0-beta.27 for testing purposes. The blockchain is mining and has two users, now I would like to subscribe to events in the blockchain and perform some actions. The code is below:

var Web3 = require("web3");     

var ether_port = 'http://localhost:8545'
var web3       = new Web3(new Web3.providers.HttpProvider(ether_port));

web3.eth.subscribe("pendingTransactions"
                  , function(err, result){
    if (err){ console.log(err) }
    else { console.log("result: ", result) }
});

I am getting the following error :

Error: The current provider doesn't support subscriptions: HttpProvider
at Subscription.subscribe

Kindly Help.

Answer 1

As the error suggests, pub/sub is not available over HTTP. However, you can use it over WS. 

This documentation -> https://web3js.readthedocs.io/en/1.0/web3-eth-subscribe.html states that we can use the function, but it omits the provider portion of the code.

Try starting your nodes using web socket connections (geth --ws --wsport 8545 ..., assuming you're using geth), and change to a WebsocketProvider.

var Web3 = require("web3");     

var ether_port = 'ws://localhost:8545'
var web3       = new Web3(new Web3.providers.WebsocketProvider(ether_port));

web3.eth.subscribe("pendingTransactions"
                  , function(err, result){
    if (err){ console.log(err) }
    else { console.log("result: ", result) }
});