🦄 Uniswap V2 Pool Event Listening

Uniswap V2 is a decentralized exchange protocol that allows users to trade tokens without the need for a trusted intermediary. By listening to pool events in Uniswap V2, developers can gain insights into key actions such as swaps, liquidity provision, and token burns/mints, helping them create applications with real-time data updates.

📦 Overview

This repository provides examples of how to listen for various events in a Uniswap V2 pool using ethers v5.7.2 and ethers v6.0.0.
It works across most EVM-compatible chains, but if you experience any issues, feel free to reach out for assistance.

✅ Requirements

1. Rename .env.example to .env and provide the following environment variables:

   • WSS_PROVIDER_URL: WebSocket URL for your provider (e.g., Infura, Alchemy).
   • POOL_ADDRESS: The address of the Uniswap V2 pool.
   • EVENT_NAME: The event you want to listen to (see below for event names).

2. Install project dependencies by running the following command:

   npm install

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📜 Pool Events in Uniswap V2

Uniswap V2 pool events allow you to listen to key actions within a liquidity pool. These events can provide valuable insights for tracking liquidity, swaps, and reserves.

Event Name	Returns
Swap	(sender, amount0In, amount1In, amount0Out, amount1Out, to)
Sync	(reserve0, reserve1)
Mint	(sender, amount0, amount1)
Burn	(sender, amount0, amount1, to)

• Swap: Triggered whenever a swap happens, indicating which tokens were swapped and in what quantity.
• Sync: Triggered when the reserves of the pool are updated.
• Mint: Fired when liquidity is added to the pool.
• Burn: Fired when liquidity is removed from the pool.

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🔊 Pool Listening Functions

ethers v5

In ethers v5, the following methods are used to listen for events emitted by the pool:

• pool.on(eventName, listener): Listen for an event continuously, reacting to every occurrence of the event.
• pool.once(eventName, listener): Listen for an event once, then stop listening after the first occurrence.
• pool.off(eventName, listener): Remove a specific listener for an event, stopping it from receiving future events.
• pool.removeListener(eventName, listener): Alias for off, removing a specific listener.
• pool.removeAllListeners(eventName): Remove all listeners for a specific event.

ethers v6

In ethers v6, the API is slightly adjusted, but the functionality remains similar:

• pool.addListener(eventName, listener): Listen for an event continuously (alias for on).
• pool.on(eventName, listener): Same as addListener, listens continuously.
• pool.once(eventName, listener): Listen for an event once, then stop.
• pool.off(eventName, listener): Remove a specific listener from an event.
• pool.removeListener(eventName, listener): Alias for off, removes a specific listener.
• pool.removeAllListeners(eventName): Remove all listeners for a specific event.

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📊 Pool Listener Info

The following methods allow you to query listener information:

Method	Description
pool.listeners(eventName)	Returns an array of listeners registered for the event.
pool.listenerCount(eventName)	Returns the number of listeners registered for the event.

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🗂️ Query Historical Pool Event Data

To query past events in the pool's history, use the following methods.

ethers v5

• pool.queryFilter(eventName, fromBlock, toBlock):
  • Fetches historical event data for a specific event.
  • Parameters:
    • eventName: The event you want to query (optional).
    • fromBlock (default: 0): The starting block number for the query.
    • toBlock (default: "latest"): The ending block number for the query.

ethers v6

• pool.queryFilter(eventName, fromBlock, toBlock): Same as v5, used to fetch historical events.
• pool.getEvent(eventName):
  • Returns the event object for a given name.
  • Use Case: Helpful when event names conflict with JavaScript reserved words or for programmatically accessing contract events.

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