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I'm a little bit noob, so bear with me, but I love the blockchain very much and that's why I'm here, so please hear/help me out. I am building a price scanner for Uniswap, so I have this program to check the price of DAI/WETH on Uniswap that runs just fine:

const { ChainId, Fetcher, WETH, Route, Trade, TokenAmount, TradeType, Percent } = require('@uniswap/sdk');
const ethers=require('ethers');
const chainId = ChainId.MAINNET;
const daiAddress = '0x6b175474e89094c44da98b954eedeac495271d0f';


const init = async () => {
    const dai = await Fetcher.fetchTokenData(chainId, daiAddress);
    const weth = WETH[chainId];
    const pair = await Fetcher.fetchPairData(dai, weth);
    const route = new Route([pair], weth);
    const trade = new Trade(route, new TokenAmount(weth, '100000000000000000'), TradeType.EXACT_INPUT);

    console.log(route.midPrice.toSignificant(6));

However, if I want to create a for loop on checking the price of more than one token, I add another token in a for loop, but node.js throws me an error: (node:8368) UnhandledPromiseRejectionWarning: Error: Invariant failed: CHAIN_ID

Here is the code:

const { ChainId, Fetcher, WETH, Route, Trade, TokenAmount, TradeType, Percent } = require('@uniswap/sdk');
 const ethers=require('ethers');
 const chainId = ChainId.MAINNET;
 const daiAddress = '0x6b175474e89094c44da98b954eedeac495271d0f';
 const sushiAddress = '0x6b3595068778dd592e39a122f4f5a5cf09c90fe2';


const init = async () => {
    const dai = await Fetcher.fetchTokenData(chainId, daiAddress);
    const sushi = await Fetcher.fetchTokenData(chainId, sushiAddress)
    tokens = [dai, sushi];
    const weth = WETH[chainId];
    for (token in tokens) {
    const pair = await Fetcher.fetchPairData(token, weth);
    }
    const route = new Route([pair], weth);
    const trade = new Trade(route, new TokenAmount(weth, '100000000000000000'), TradeType.EXACT_INPUT);
    console.log(route.midPrice.toSignificant(6));

How do I create a correct for loop that would check the tokens I type in?

Much love if you can help a n00b out on his path to the glorious web3 matrix <3

1

Change this:

for (token in tokens)

To this:

for (token of tokens)

It's a common mistake in Javascript (which has nothing to do with Ethereum, by the way).

3
  • Thanks so much!!!! I come from a Python background (well, not really a background, just thought learning Python was better for the blockchain, but soon realized node.js is the way to go), and in Python the loop goes for/in, not for/of! Haha, thanks , it works beautifully now (just needed to move the constants pair and trade to the local scope of the function). :************ – Teo Dec 4 '20 at 13:47
  • @Teo: NP, feel free to accept my answer by clicking on the V next to it. – goodvibration Dec 4 '20 at 13:58
  • Boom, goodvibrations, you da best – Teo Dec 4 '20 at 14:15

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