How can I get the correct pair price from Uniswap v3 pool?

Question

Code showing me token price in wrong format. How to solve it?

From the code I got:

1 WETH = -3.30628482e-9 USDC

1 USDC = -302454281.60057910558352924961 WETH

But the real/expected values were:

1 WETH = 3306.2848 USDC

1 USDC = 0.000302 WETH

Here's the code:

const Web3 = require('web3');
const { BigNumber } = require('bignumber.js');
const UniswapV3PoolABI = require('./abis/UniswapV3PoolABI.json');

// Pool address and pair addresses
const POOL_ADDRESS = '0x88e6A0c2dDD26FEEb64F039a2c41296FcB3f5640';
const WETH_ADDRESS = '0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2';
const USDC_ADDRESS = '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48';

// RPC URL
const RPC_URL = 'wss://ethereum-rpc.publicnode.com';

// Initialize Web3 with WebSocketProvider
const web3 = new Web3(new Web3.providers.WebsocketProvider(RPC_URL));

// Initialize contract
const uniswapV3PoolContract = new web3.eth.Contract(UniswapV3PoolABI, POOL_ADDRESS);

// Subscribe to Swap event
uniswapV3PoolContract.events.Swap({}, (error, event) => {
    if (error) {
        console.error('Error:', error);
        return;
    }

    const { returnValues } = event;

    //console.log('Event data:', returnValues);

    const amount0In = new BigNumber(returnValues.amount0);
    const amount1In = new BigNumber(returnValues.amount1);

    //console.log('Raw amounts:');
    //console.log(`Amount0: ${amount0In.toString()} WETH`);
    //console.log(`Amount1: ${amount1In.toString()} USDC`);

    // Check if amounts are valid
    if (!amount0In.isFinite() || !amount1In.isFinite() || amount0In.isZero() || amount1In.isZero()) {
        console.error('Invalid amounts:', amount0In.toString(), amount1In.toString());
        return;
    }

    // Calculate the price
    const price = amount0In.div(amount1In).toString(); // Price in WETH per USDC

    //console.log(`Current WETH/USDC Price: ${price} WETH per USDC`);
    console.log(`1 WETH = ${price} USDC`);
    console.log(`1 USDC = ${new BigNumber(1).div(price).toString()} WETH`);
})
.on('connected', () => console.log('Connected to Ethereum node'))
.on('error', (error) => console.error('Error in contract event subscription:', error));

Answer 1

You can remove the negative sign by using Math.abs(). Since the USDC value is in 6-decimal format and WETH value is in 18-decimal format as per their respective token contracts, so the USDC value needs to be converted to 18-decimals as well in order to calculate the price by dividing.

The revised portion of the code would be:

const usdcDecimals = 6;

// Removing negative sign by using Math.abs()
const absoluteUsdcValue = Math.abs(amount0In);  // Needs to be converted in Wei as USDC is having 6-decimals
const absoluteWethValue = Math.abs(amount1In);  // Already in Wei as WETH is having 18-decimals

// Converting USDC value to Wei (i.e., 18-decimals)
const usdcValueInEther = parseFloat(absoluteUsdcValue) / Math.pow(10, usdcDecimals);
const usdcValueInWei = parseFloat(web3.utils.toWei(usdcValueInEther.toString(), 'ether'));

// Calculate the price
const price = BigNumber(absoluteWethValue).div(BigNumber(usdcValueInWei)).toString(10); // Price in WETH per USDC 

console.log(`Current WETH/USDC Price: ${price} WETH per USDC`);
console.log(`1 USDC = ${price} WETH`);
console.log(`1 WETH = ${BigNumber(1).div(price).toString()} WETH`);

Output: