TLDR:

• Set up a node.js script using web3.js to connect to Ethereum via Chainstack endpoints.
• Fetch real-time crypto prices through Chainlink’s AggregatorV3Interface contracts, removing reliance on external APIs.
• Conversion involves retrieving integer values from the contract and formatting them into human-readable outputs.
• Call prices at intervals to keep data updated without single-point-of-failure risks.

​

Main article

In today’s digital age, accessing real-time and reliable cryptocurrency data is crucial for many applications. While many resort to third-party APIs, these can sometimes introduce risks, such as downtime, potential manipulation, or sudden discontinuation of services. Chainlink, a decentralized oracle network, solves this dilemma as a dependable bridge between on-chain and off-chain data. Paired with the robust infrastructure of an Ethereum node hosted by Chainstack, we can further enhance the reliability of our data source.

One advantage of this approach is using decentralized exchange (DeX) oracles, which largely eliminates the risk of relying on single-point-of-failure third-party APIs. This ensures uninterrupted access to critical crypto pricing data and fosters a decentralized ethos in our applications.

In this guide, we’ll demonstrate how to harness the power of Chainlink oracles by using a Chainstack Ethereum node to fetch real-time crypto prices from the network, giving you a resilient and dependable data source.

​

Setting the scene

For our purpose, we’ll use node.js alongside the web3.js library, allowing us to communicate with the Ethereum blockchain. We aim to fetch prices for five cryptocurrencies: BTC, ETH, LINK, BNB, and LTC against USD.

​

Prerequisites

• node.js library
• web3.js library
• Contract addresses of pairs you’re interested in
• A Chainstack Ethereum node

​

Get an Ethereum node

Follow these steps to deploy an Ethereum node:

​

Install web3.js

Create a new project in a directory and open a terminal, then run:

npm i web3

​

The code

In the same directory, create a new file named index.js and paste the following code:

const { Web3 } = require("web3");

const web3 = new Web3(
	"YOUR_CHAINSTACK_ENDPOINT"
);

// Object with the smart contracts for the pairs
const pairs = {
	"BTC / USD": "0xF4030086522a5bEEa4988F8cA5B36dbC97BeE88c",
	"ETH / USD": "0x5f4eC3Df9cbd43714FE2740f5E3616155c5b8419",
	"LINK / USD": "0x2c1d072e956AFFC0D435Cb7AC38EF18d24d9127c",
	"BNB / USD": "0x14e613AC84a31f709eadbdF89C6CC390fDc9540A",
	"LTC / USD": "0x6AF09DF7563C363B5763b9102712EbeD3b9e859B",
};

// aggregatorV3Interface ABI
const aggregatorV3InterfaceABI = [
	{
		inputs: [],
		name: "decimals",
		outputs: [{ internalType: "uint8", name: "", type: "uint8" }],
		stateMutability: "view",
		type: "function",
	},
	{
		inputs: [],
		name: "description",
		outputs: [{ internalType: "string", name: "", type: "string" }],
		stateMutability: "view",
		type: "function",
	},
	{
		inputs: [{ internalType: "uint80", name: "_roundId", type: "uint80" }],
		name: "getRoundData",
		outputs: [
			{ internalType: "uint80", name: "roundId", type: "uint80" },
			{ internalType: "int256", name: "answer", type: "int256" },
			{ internalType: "uint256", name: "startedAt", type: "uint256" },
			{ internalType: "uint256", name: "updatedAt", type: "uint256" },
			{ internalType: "uint80", name: "answeredInRound", type: "uint80" },
		],
		stateMutability: "view",
		type: "function",
	},
	{
		inputs: [],
		name: "latestRoundData",
		outputs: [
			{ internalType: "uint80", name: "roundId", type: "uint80" },
			{ internalType: "int256", name: "answer", type: "int256" },
			{ internalType: "uint256", name: "startedAt", type: "uint256" },
			{ internalType: "uint256", name: "updatedAt", type: "uint256" },
			{ internalType: "uint80", name: "answeredInRound", type: "uint80" },
		],
		stateMutability: "view",
		type: "function",
	},
	{
		inputs: [],
		name: "version",
		outputs: [{ internalType: "uint256", name: "", type: "uint256" }],
		stateMutability: "view",
		type: "function",
	},
];

let conversionRate = {};

async function fetchPrices() {
	try {
		for (let pair in pairs) {
			// Smart contract instance
			const priceFeed = new web3.eth.Contract(
				aggregatorV3InterfaceABI,
				pairs[pair]
			);

			// use eth_call
			const roundData = await priceFeed.methods.latestRoundData().call();
			// Chainlink returns price data with 8 decimal places for accuracy.
			// We divide by 1e8 to convert it to a human-readable format.
			const price = Number(roundData.answer) / 1e8;
			conversionRate[pair] = price.toFixed(2);
		}

		console.log("Prices fetched:", conversionRate);
	} catch (error) {
		console.error("Error fetching prices:", error);
	}
}

// Fetch prices initially and then at regular intervals
fetchPrices();
setInterval(fetchPrices, 60 * 1000); // Fetch every minute

Add your Chainstack Ethereum endpoint to web3, save and run node index in the terminal; the console will display an object with the most up-to-date prices.

Prices fetched: {
  'BTC / USD': '29385.26',
  'ETH / USD': '1848.97',
  'LINK / USD': '7.51',
  'BNB / USD': '240.95',
  'LTC / USD': '83.65'
}

​

Understanding the code

The script starts by importing the web3 library and creating an instance to an Ethereum node, then the bulk of the logic is as follows:

1. Specify the Chainlink price feeds. Ethereum smart contracts represent Chainlink’s decentralized price feeds. Each cryptocurrency price feed has a unique contract address. Our script stores these addresses in the pairs dictionary with the cryptocurrency pair name as the key. You can find additional price feed contract addresses on Chainlink’s Price Feed Contract Addresses.

2. Specify the Chainlink price feed contract addresses.

   Chainlink’s decentralized price feeds are represented through smart contracts. Each price feed for a specific cryptocurrency pair is associated with a unique contract address. In our script, these addresses are stored in a dictionary named pairs, where the key is the name of the cryptocurrency pair. Refer to Chainlink’s Price Feed Contract Addresses page for additional price feed contract addresses.

3. The aggregatorV3Interface ABI.

   We add the aggregatorV3Interface ABI required to interact with the smart contract. The ABI outlines the functions in the smart contract so the library knows how to use them.

4. Interact with Chainlink price feeds.

   Chainlink price feeds are implemented using the AggregatorV3Interface, which provides several functions for data interaction. Among these functions, latestRoundData is the one we use to fetch the latest price information. For a complete reference to the functions and capabilities of the AggregatorV3Interface, you can consult Chainlink’s API Reference page.

5. Fetching the Prices.

   In our fetchPrices function, we iterate through the specified pairs, and for each pair:

   • Create an instance of the Chainlink price feed contract using the web3.js library.
   • Call the latestRoundData function to retrieve the most recent price data.
   • Convert the obtained price to a readable format (divide by 1e8 and round to two decimal places) and store it in our conversionRate dictionary.

6. Continual data refresh.

   To ensure we continually have up-to-date price information, we call our fetchPrices function every minute using JavaScript’s setInterval function.

​

Conclusion

Following the above steps, you’ve successfully built a robust and lightweight script to fetch real-time cryptocurrency prices directly from the Ethereum blockchain, eliminating the need for third-party APIs or services. With this approach, you ensure data accuracy and gain unparalleled control over how you fetch and manage this data. Happy coding and trading!

​

About the author

Edin Drazevicanin

Technical Support Engineer @ Chainstack

JUST BUIDL IT!