ETH Fetch

A JavaScript interface for fetching data from Ethereum nodes and smart contracts.

The eth-fetch library is a JavaScript interface designed for fetching data from Ethereum nodes and smart contracts using read-only JSON-RPC calls. To get started, install the library:

npm install eth-fetch

ethFetch Methods

The library supports two methods, one for creating a provider instance for sending JSON-RPC requests over HTTP, and the other for creating an interface for smart contract interactions based on a contract address and ABI.

ethFetch.RpcProvider(providerUrl);

Creating a provider instance is supported by the ethFetch.RpcProvider(); method, and requires a providerUrl parameter be provided, which expects a provider. The provider should support a JSON-RPC interface over HTTP (e.g.. port 8545 of a Geth node, an endpoint for a service like Infura).

ethFetch.Contract(provider, address, abi);

Creating a contract interface is supported by the ethFetch.Contract(); method, and requires a provider, address, and abi parameter be provided. These should correspond to a provider instance (such as ethFetch.RpcProvider), a the contract's address, and the contract's ABI. The ABI encoding/decoding is supported by @ethersproject/abi, therefore the ABI supplied must match an ABI Format supported by Ethers.

Contract ABI Methods

A number of methods is made available via the contract interface for Ethereum smart contract interactions. This includes handling for encoding and decoding of function calls, responses, event topics, and logs. This also includes extracting metadata about functions and events, and ABI parsing. This functionality is supported by @ethersproject/abi.

.abi.encodeFunctionCall(functionName, params);
.abi.decodeFunctionResponse(functionName, data);

.abi.encodeParams(types, values);
.abi.decodeParams(types, data);

.abi.encodeEventTopics(eventName, params);
.abi.decodeEventLog(eventName, log);

.abi.getFunctionSelector(functionName);

.abi.parseAbi();

Example Use

In this first example, a provider instance is created, and used to fetch the current block number.

const ethFetch = require('eth-fetch');

// Create instance of the provider
const providerUrl = "https://mainnet.infura.io/v3/INFURA_API_KEY";
const provider = new ethFetch.RpcProvider(providerUrl);

// Fetch current Block Number
(async () => {
    try {
        const blockNumber = await provider.request({ method: 'eth_blockNumber' });
        console.log("Block Number:", parseInt(blockNumber, 16));
    } catch (error) {
        throw error;
    }
})();

// Sample Output:
// Block Number: 21589526

In this second example, an interface for an Ethereum Name Service smart contract is created, supplying the contract address, and ABI for the owner function, to retrieve the owner address for the ENS name ethereum.eth.

const ethFetch = require('eth-fetch');

// Create instance of the provider
const providerUrl = "http://127.0.0.1:8545";
const provider = new ethFetch.RpcProvider(providerUrl);

// Create smart contract interface
const contractAddress = "0x00000000000C2E074eC69A0dFb2997BA6C7d2e1e";
const abi = ["function owner(bytes32 node) external view returns (address)"];
const contract = new ethFetch.Contract(provider, contractAddress, abi);

// Find the owner address for ethereum.eth (using namehash)
const namehash = "0x78c5b99cf4668cf6da387866de4331c78b75b7db0087988c552f73e1714447b9";

(async () => {
    try {
        const ownerAddress = await contract.owner(namehash);
        console.log("Owner Address:", ownerAddress);
    } catch (error) {
        throw error;
    }
})();

// Sample Output:
// Owner Address: [ '0xAd2e180019FCa9e55CADe76E4487F126Fd08DA34' ]