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We now support ability to factor tx cost into the quotes
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@joshstevens19 joshstevens19 released this 04 Aug 16:28
· 39 commits to master since this release
3.4.0
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Learn about vigilant mode.

A lovely feature has been added:

Including gas fees in the trade response

The library has the ability to work out the best trade including gas fees. As expected this does add around about 700MS onto the response time due to the need to have to query eth_estimateGas an the top 3 quotes to work out the best result. How it works is:

  • It gets the best expected trade quotes as it normally does
  • IF you do not have enough balance or enough allowance it will not estimate gas because it be a always failing transaction and the node will throw an error.
  • ALSO IF the token your swapping does not have a fiat price in coin gecko then again it ignores the below as it can not do the math without a base currency.
  • IF you have enough balance and allowance then finds the best 3 of the different hop options:
    • best direct trade aka ETH/TOKEN > TOKEN_YOU_WANT
    • best trade which jumps 2 hops aka ETH/TOKEN > TOKEN > TOKEN_YOU_WANT
    • beat trade which jumps 3 hops aka ETH/TOKEN > TOKEN > OTHER_TOKEN > TOKEN_YOU_WANT
  • It then eth_estimateGas those 3 transactions and takes off the tx fee from the expected quote
  • It then returns the trade which is the highest left amount, meaning it has taken into consideration gas within the quote

Do not worry if you want to use this feature but worried that first time customers before they approve ability for uniswap to move the tokens will not be able to benefit from this, as soon as you have approved uniswap to be able to move tokens on their behalf a new trade will be emitted within the quoteChanged$ stream so you can still get all the benefit on first time swaps.

The beauty of this is its very easy to setup just pass in a gasSettings object including a getGasPrice async function (IT MUST BE A PROMISE) which returns the gas price in Gwei which you want to use for the working out. This must be a string number aka 30 = 30 Gwei it does not handle passing in hex strings. This can be dynamic aka we call this everytime we go and work out the trades, so if you want this to hit an API or etherscan or return a fixed gas price, its completely up to you.

import {
  ChainId,
  TradeContext,
  UniswapPair,
  UniswapPairSettings,
} from 'simple-uniswap-sdk';
const uniswapPair = new UniswapPair({
  // the contract address of the token you want to convert FROM
  fromTokenContractAddress: '0x419D0d8BdD9aF5e606Ae2232ed285Aff190E711b',
  // the contract address of the token you want to convert TO
  toTokenContractAddress: '0x1985365e9f78359a9B6AD760e32412f4a445E862',
  // the ethereum address of the user using this part of the dApp
  ethereumAddress: '0xB1E6079212888f0bE0cf55874B2EB9d7a5e02cD9',
  // you can pass in the provider url as well if you want
  // providerUrl: YOUR_PROVIDER_URL,
  // OR if you want to inject your own ethereum provider (no need for chainId if so)
  // ethereumProvider: YOUR_WEB3_ETHERS_OR_CUSTOM_ETHEREUM_PROVIDER,
  chainId: ChainId.RINKEBY,
  settings: new UniswapPairSettings({
    gasSettings: {
      getGasPrice: async () => {
        return 'GWEI_GAS_PRICE';
      },
    },
  }),
});

That's it now you get trades which bring you back the best trades minus the tx cost.

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