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I'm new in the blockchain technology, moreover in some dev tasks related to the blockchain. Nevertheless, suddnely I was asked to implement such a demo back-end Node.js app that:

Task: Get information about all tokens for some wallet address.

For example:

Input: The wallet address is: 0xB245ac044E3c2e9781C9c848249E2e6b186b080F

Output:

ERC-20 tokens: USDT $100, USDC $200, SHIB $300;
Etherum native token: ETH $500.

I'm not asking about ready-to-use code snippet (but why not?), rather it would be better to know which steps should be proceeded in general using Node.js and Web3.js specifics.

Where I've tried to find the answer:

Each of these helps to understand some moments, but the whole solution is still not obvious for me.

It is very possible that I am missing something for input, also possible that my output is incorrect in some moments. But I hope the general idea of the question is clear more or less.

Volodymyr Nabok
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1 Answers1

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I'll split your question into several steps, as there is no simple way to fetch the data from the blockchain in the format you want, so you have to "walk a thorny path".

1. Get the list of Token Addresses owned by an Externally-Owned-Account
1.1 Query for Transfer events

A token, or better to say - a contract, which implements the ERC20 interface, emits an event Transfer(address from, address to, uint256 amount) Event every time the token transfer occurs. You can query the blockchain for the past events, where the to is your target account. The event emitters are the contracts, possibly the ERC20 tokens, but also those could be the ERC721 tokens, as they have the same event signature in the interface.

Also notice, an event emitter could be any contract, even not related to tokens, as any contract can emit any event.

Some blockchain nodes could limit the block ranges per request to get the events from, so you have to implement the pagination, as you want to get events from block 0 to latest

1.2 Find out the ERC20 Tokens

You have here several options

a. You can create the list of known tokens from various 3rd party sources (CoinmarketCap, 1inch, Shushiswap, Uniswap) and then filter those Transfer emitters narrowed to those from the known list.

b. Another option, is to fetch ERC20 interface Information directly from the blockchain. Call each Transfer emitter by getting the decimals, name, symbol, balanceOf. If you don't get the exception for the calls, then the contract is highly likely the ERC20 token.

c. Or you can get the contracts ABI (if the contract is validated) from Etherscan, and check if everything from ERC20 interface exists in the ABI.

I have implemented all these steps in the 0xweb cli tool, which uses the dequanto library. You can check the implementation in CTokens.ts#L88

After these steps, you'll get the list of all tokens owned by the account, and their amounts (balanceOf).

2. Get the token prices

Another challenging task, in case you don't use any 3rd party service and stick to onchain data.

a. Query the oracle price feeds like chain.link. But not all tokens are presented there.

b. Get the price directly from DEX, like uniswap, sushiswap, pancakeswap etc. But surprise - no easy way to get the price also here. You can find a stable pair (Some USD stable coin/Your Token), if the pair exists just grab the reserves and the ratio is the price. For less popular tokens there could be only the ETH/YourToken pair, and the price for ETH you can get these steps a) or b).

I've written a more in-depth article: https://dev.kit.eco/ethereum-get-token-price-at-a-specific-block-onchain on how to get the price at any time in the past. And if you don't have the archive node, you just get the price for the latest block.

If you want me to explain some parts in detail, don't hesitate to ask in the comments, I'll update the answer then.

tenbits
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