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Fetching Data

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While the SDK is fully self-contained, there are two cases where it needs on-chain data to function. This guide will detail both of these cases, and offer a sample that you can use to fetch this data.

Case 1: Tokens

Unsurprisingly, the SDK needs some notion of an ERC-20 token to be able to function. This immediately raises the question of where data about tokens comes from.

As an example, let's try to represent DAI in a format the SDK can work with. To do so, we need at least 3 pieces of data: a chainId, a token address, and how many decimals the token has. We also may be interested in the symbol and/or name of the token.

Identifying Data

The first two pieces of data — chainId and token address — must be provided by us. Thinking about it, this makes sense, as there's really no other way to unambiguously identify a token.

So, in the case of DAI, we know that the chainId is 1 (we're on mainnet), and the token address is 0x6B175474E89094C44Da98b954EedeAC495271d0F. Note that it's very important to externally verify token addresses. Don't use addresses from sources you don't trust!

Required Data

The next piece of data we need is decimals.

Provided by the User

One option here is to simply pass in the correct value, which we may know is 18. At this point, we're ready to represent DAI as a Token:

import { ChainId, Token } from '@uniswap/sdk-core'

const chainId = ChainId.MAINNET
const tokenAddress = '0x6B175474E89094C44Da98b954EedeAC495271d0F' // must be checksummed
const decimals = 18

const DAI = new Token(chainId, tokenAddress, decimals)

If we don't know or don't want to hardcode the value, we could look it up ourselves via any method of retrieving on-chain data in a function that looks something like:

import { ChainId } from '@uniswap/sdk-core'

async function getDecimals(chainId: ChainId, tokenAddress: string): Promise<number> {
// Setup provider, import necessary ABI ...
const tokenContract = new ethers.Contract(tokenAddress, erc20abi, provider)
return tokenContract["decimals"]()

Optional Data

Finally, we can talk about symbol and name. Because these fields aren't used anywhere in the SDK itself, they're optional, and can be provided if you want to use them in your application. However, the SDK will not fetch them for you, so you'll have to provide them:

import { ChainId, Token } from '@uniswap/sdk-core'

const DAI = new Token(ChainId.MAINNET, '0x6B175474E89094C44Da98b954EedeAC495271d0F', 18, 'DAI', 'Dai Stablecoin')

Case 2: Pairs

Now that we've explored how to define a token, let's talk about pairs. To read more about what Uniswap pairs are, see Pair

As an example, let's try to represent the DAI-WETH pair.

Identifying Data

Each pair consists of two tokens (see previous section). Note that WETH used by the router is exported by the SDK Core as WETH9.

Required Data

The data we need is the reserves of the pair. To read more about reserves, see getReserves.

Provided by the User

One option here is to simply pass in values which we've fetched ourselves to create a Pair. In this example we use ethers to fetch the data directly from the blockchain:

import { ChainId, Token, WETH9, CurrencyAmount } from '@uniswap/sdk-core'
import { Pair } from '@uniswap/v2-sdk'

const DAI = new Token(ChainId.MAINNET, '0x6B175474E89094C44Da98b954EedeAC495271d0F', 18)

async function createPair(): Promise<Pair> {
const pairAddress = Pair.getAddress(DAI, WETH9[DAI.chainId])

// Setup provider, import necessary ABI ...
const pairContract = new ethers.Contract(pairAddress, uniswapV2poolABI, provider)
const reserves = await pairContract["getReserves"]()
const [reserve0, reserve1] = reserves

const tokens = [DAI, WETH9[DAI.chainId]]
const [token0, token1] = tokens[0].sortsBefore(tokens[1]) ? tokens : [tokens[1], tokens[0]]

const pair = new Pair(CurrencyAmount.fromRawAmount(token0, reserve0), CurrencyAmount.fromRawAmount(token1, reserve1))
return pair

Note that these values can change as frequently as every block, and should be kept up-to-date.