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Version: 2.2

Get Started with eth_getLogs Through Moralis: Complete Guide

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Insights into events occurring on the Ethereum blockchain are crucial for blockchain developers. Accessing this valuable data is made simpler with eth_getLogs, and one of the tools for this purpose is the getContractLogs endpoint from Moralis.

Thanks to the Moralis SDK, fetching and analyzing event logs on Ethereum is easy, and if you want to learn how to retrieve and analyze Ethereum event logs using the SDK, this guide will be highly beneficial. It includes practical JavaScript examples, and compares Moralis' getContractLogs endpoint with the eth_getLogs RPC call to help you make informed decisions.

tip

For a step-by-step tutorial on obtaining contract logs using the Moralis blockchain API, read the Get logs for contract article.

The Gateway to Ethereum Events with eth_getLogs​

The eth_getLogs is a JSON-RPC method in Ethereum that returns event data as an array of all logs matching a specified filter object. It is a fundamental method for querying and retrieving event logs from the Ethereum blockchain.

The utilization of eth_getLogs plays a vital role in the blockchain industry as it empowers developers with a valuable tool to monitor and analyze events occurring on the Ethereum blockchain. Throughout this guide, we will delve into the functions and benefits of this tool and look at the advantages of using Moralis instead.

Also, transaction receipts serve as repositories for Ethereum event logs, capturing details such as gas consumption, transaction status, and more. Understanding storage dynamics allows us to efficiently retrieve this information using methods like eth_getLogs along with other alternatives.

Unveiling the Efficiency of Moralis' getContractLogs Endpoint​

The getContractLogs endpoint from Moralis stands as a hallmark of convenience, offering an effective way to access ETH get logs. Before diving into Moralis, let's see how Moralis' getContractLogs compares against eth_getLogs.

Moralis’ getContractLogs vs eth_getLogs: Comparative Analysis​

The eth_getLogs RPC call, akin to getContractLogs, allows fetching logs through filter objects which encapsulate parameters like fromBlock, toBlock, and address to define the range and source of logs. Although quite powerful, eth_getLogs requires a more detailed setup with JSON RPC calls, which might become quite complicated compared to the user-friendly, single API call facilitated by Moralis.

That said, the setup for eth_getLogs involves parameter settings as illustrated here:

curl -X POST --data '{"jsonrpc":"2.0","method":"eth_getLogs","params":[{"topics":["0x000000000000000000000000a94f5374fce5edbc8e2a8697c15331677e6ebf0b"]}],"id":74}'

It is essential to evaluate the comprehensive filtration options rendered by eth_getLogs against the simplified, user-friendly approach of Moralis, aligning with the project's necessities.

A Practical Approach: JavaScript Example using Moralis​

To highlight how to get started with Moralis, we present a JS script below illustrating how to employ the Moralis SDK for querying Ethereum contract logs:

import Moralis from 'moralis';

try {
  // Initializing the Moralis SDK with your unique API key
  await Moralis.start({
    apiKey: "YOUR_API_KEY"
  });

  // Executing the getContractLogs method to retrieve contract logs
  // Here, we target the Ethereum mainnet, denoted by the "chain" parameter set to "0x1".
  // You can modify this parameter to target other networks as per your requirements.
  // The "address" parameter specifies the contract address for fetching the logs.
  const response = await Moralis.EvmApi.events.getContractLogs({
    "chain": "0x1",
    "address": "0xb47e3cd837dDF8e4c57F05d70Ab865de6e193BBB",
    "topic0": "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"
  });

  // Logging the response enables you to inspect and understand the structure of the data retrieved.
  console.log(response);
} catch (e) {
  // Any errors arising during the execution are caught here, facilitating a clean error-handling process.
  console.error(e);
}

Deciphering the Script: In this segment, we dissect each part of the script to offer a deep understanding of utilizing the Moralis library effectively:

  • Import and initialization: Start by importing the Moralis library and initializing the SDK using your API key.
  • Log retrieval: This part describes how to retrieve contract logs using defined parameters.
  • Response and error handling: This section underlines the response logging and error management process.

Creating Real-World Applications​

Embark on a hands-on tutorial to build applications capable of querying Ethereum smart contract event logs utilizing Moralis.

In this step-by-step guide, you will learn how to create a NodeJS and NextJS application to query Ethereum smart contract event logs using Moralis. Understanding the backend and frontend code in their respective breakdown sections will help you understand the overall structure and functionality of the application.

Step 1: Cloning and Setting Up the Project​

Using the Moralis Events API, you will build a robust application capable of querying ant Ethereum smart contract event logs. Now, the steps to setting up the project include cloning the project from a GitHub repository and installing the necessary Node packages:

npm i moralis @moralisweb3/common-evm-utils dotenv express

Step 2: Backend Code Breakdown​

Dive into the backend construction using Express and the Moralis SDK. The following example outlines how to set up an Express server and define a route to handle the logs retrieval:

const express = require("express");
const app = express();
const port = 5001;
const Moralis = require("moralis").default;
const cors = require("cors");
require("dotenv").config({ path: ".env" });
app.use(cors());
app.use(express.json());

const MORALIS_API_KEY = process.env.MORALIS_API_KEY;

app.get("/getlogs", async (req, res) => {
  try {
    const { query } = req;
    const response = await Moralis.EvmApi.events.getContractLogs({
      address: query.address,
      chain: query.chain,
      topic0: query.topic0,
    });
    return res.status(200).json(response);
  } catch (e) {
    console.log(`Something went wrong ${e}`);
    return res.status(400).json();
  }
});

Moralis.start({
  apiKey: MORALIS_API_KEY,
}).then(() => {
  app.listen(port, () => {
    console.log(`Listening for API Calls`);
  });
});

Step 3: Frontend Code Breakdown​

The following example shows how to send a request to the backend localhost API:

const API_URL = "http://localhost:5001/getlogs";
const ADDRESS = "0xb47e3cd837dDF8e4c57F05d70Ab865de6e193BBB";
const CHAIN = "0x1";
const TOPIC0 = "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef";

const endpoint = `${API_URL}?address=${ADDRESS}&chain=${CHAIN}&topic0=${TOPIC0}`;

fetch(endpoint, { method: 'GET' })
  .then(response => response.text())
  .then(result => console.log(result))
  .catch(error => console.log('Error:', error.message));

You now possess the knowledge to build a more complex application by expanding upon this basic structure.

Get Started with eth_getLogs: Summary​

Having navigated through the potentials and the intricate workings of ETH get logs, you are now equipped with the knowledge and practical experience to integrate Moralis' getContractLogs endpoint into your projects. Leveraging Moralis not only simplifies the process but also enhances the efficiency, allowing you to focus on building stellar applications in the blockchain space.