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July 29, 2022

Uniswap V3 SDK Swap Tutorial 4/5 – Get swap route

This is the part 4 of Uniswap V3 SDK Swap Tutorial, full source code.

A crucial part of making a swap is creating a swap route. This is the optimal path with swap parameters which Uniswap constructs to make the desired swap.

How to conduct token swap in Uniswap

Swap is conducted in the following way:

  1. You first ask Uniswap for a swap route with desired parameters.
  2. Uniswap gives you that route that includes:
    1. Path on how swap would be made optimally. For example, if swap WETH->USDT is to be made, a path WETH->DAI->USDT can be more optimal to get more USDT for a given amount of WETH.
    2. Optimal quote.
    3. Swap gas and gas price estimations.
    4. And many other parameters.
  3. If you are fine with that quote you submit swap transaction with that route and wait for result.

Let’s see what we need to specify to ask Uniswap for a route:

Uniswap AlphaRouter and route loading

After this explanation it should be straightforward. First, let’s ask Uniswap for a route and check if route is returned:

const inAmount = CurrencyAmount.fromRawAmount(tokenIn, amountIn.toString());

const router = new AlphaRouter({ chainId: tokenIn.chainId, provider: provider });
const route = await router.route(
    // swapOptions
        recipient: walletAddress,
        slippageTolerance: new Percent(5, 100),          // Big slippage – for a test
        deadline: Math.floor(Date.now() / 1000 + 1800)    // add 1800 seconds – 30 mins deadline
    // router config
        maxSwapsPerPath: 1 // remove this if you want multi-hop swaps as well.

if (route == null || route.methodParameters === undefined)
    throw "No route loaded";

For example, on Goerli test network as of July 2022 only WETH-UNI swaps are available, so you’d get a null route trying to swap other tokens.

Then let’s print quote and gas fees:

console.log(`   You'll get ${route.quote.toFixed()} of ${tokenOut.symbol}`);
// output quote minus gas fees
console.log(`   Gas Adjusted Quote: ${route.quoteGasAdjusted.toFixed()}`);
console.log(`   Gas Used Quote Token: ${route.estimatedGasUsedQuoteToken.toFixed()}`);
console.log(`   Gas Used USD: ${route.estimatedGasUsedUSD.toFixed()}`);
console.log(`   Gas Used: ${route.estimatedGasUsed.toString()}`);
console.log(`   Gas Price Wei: ${route.gasPriceWei}`);

To those who is confused about gas and gas price like I was. Gas is the amount of computing work Ethereum needs to get the work done. Most simple swaps I tested require 300,000 of computational work and that does not change on network load. Simply put, this is a number of computation steps for Ethereum virtual machine.

Gas price is the amount in wei you pay for each computational step. If you want to speed up execution of your swap than set gas price more than estimated (route.gasPriceWei) so that nodes would be incentivised to process your operation first.

So, we finished part 4 and in this part we asked Uniswap for a swap route and got it afterwards. See part 5 on how to execute actual swap.

About Web3 and blockchain developer.
Interests: Ethereum, Uniswap and DeFi, TypeScript and Go.