Uniswap API – How to Query for Pair ID of a Chosen Token

You can use the Uniswap TheGraph for this! For example a query to get the last 10 swaps from the DAI/ETH pair would be:

{
    swaps(first: 10, where: { pair: "0xa478c2975ab1ea89e8196811f51a7b7ade33eb11" } orderBy: timestamp, orderDirection: desc) {
      transaction {
        id
        timestamp
      }
      id
      pair {
        token0 {
          id
          symbol
        }
        token1 {
          id
          symbol
        }
      }
      amount0In
      amount0Out
      amount1In
      amount1Out
      amountUSD
      to
    }
}

You can play around with queries at: https://thegraph.com/explorer/subgraph/uniswap/uniswap-v2. Integration into the frontend would happen with something like Apollo Client.

In fact this is also what the Uniswap Info is doing. It's open-source, so look around for example queries and how to use them.

For more information on how TheGraph and queries work, I just posted a blog-post about it: https://soliditydeveloper.com/thegraph.

Uniswap has an SDK through which you can fetch the gas price. See their example in their documentation :

    import { ChainId, Token, WETH, Fetcher, Route } from '@uniswap/sdk'
    
    const DAI = new Token(ChainId.MAINNET, '0x6B175474E89094C44Da98b954EedeAC495271d0F', 18)
    
    // note that you may want/need to handle this async code differently,
    // for example if top-level await is not an option
    const pair = await Fetcher.fetchPairData(DAI, WETH[DAI.chainId])
    
    const route = new Route([pair], WETH[DAI.chainId])
    
    console.log(route.midPrice.toSignificant(6)) // 201.306
    console.log(route.midPrice.invert().toSignificant(6)) // 0.00496756