# Track blockchain transactions with web3.js

By [vanDijk](https://paragraph.com/@vandijk) · 2022-05-29

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Web3 API doesn’t allow you to subscribe directly to a wallet’s incoming transactions, so to solve our particular problem, we have to use a different strategy. First, we subscribe to all pending transactions, then we filter them by the sender’s wallet address and certain other criteria.
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Web3.js allows us to talk directly to an Ethereum node via multiple protocols, including HTTP and WebSockets. For example, I use Rinkeby Testnet and nodes provided by [Infura](https://infura.io/). However, you a free to use any other provider, including local nodes.

In the function shown below, a new web3 instance with the WebSockets provider is created and used to establish a subscription to newly created transactions in blockchain. This instance is called _pending_.

A subscription object can be created using two methods, _subscribe()_ and _unsubscribe()_. Both of them accept a callback function to handle errors and any results of subscribing. There are two events that we can handle with subscriptions to pending transactions: _data_ and _error._ Certainly, _data_ is the essential event that we need for finding the transfer.

A data event handler only has one input parameter, which represents a transaction hash and checks every transaction for compliance with our search criteria when we need more details than just a hash. That’s where a different web3.js method, _getTransaction(),_ can be used for reading transaction details. As this is an asynchronous call, I simply wrap it into a try-catch statement and await for the response. You can find the response object format in the official documentation for web3 [here](https://web3js.readthedocs.io/en/1.0/web3-eth.html#gettransaction).

Once a response is received and the transaction matches our filter conditions, we need to initiate the transaction confirmation process and cancel the subscription by calling its _unsubscribe_() method. If we don’t have a transaction that satisfies our filter, we simply return from function to stay subscribed.

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*Originally published on [vanDijk](https://paragraph.com/@vandijk/track-blockchain-transactions-with-web3-js)*