Retrieve Balances

Retrieving balances involves converting an RLP encoded array of balances into a human-readable array of balances.

Implementation

1. Install omg-js, web3

To access network features from your application, use our official libraries:

Node

Requires Node >= 8.11.3 < 13.0.0

npm install @omisego/omg-js web3

Browser

You can add omg-js to a website using a script tag:

<script src="https://unpkg.com/@omisego/browser-omg-js"></script>

React Native

You can easily integrate omg-js with React Native projects. First, add this postinstall script to your project's package.json:

"scripts": {
    "postinstall": "omgjs-nodeify"
}

Then install the react native compatible library:

npm install @omisego/react-native-omg-js

2. Import dependencies

omg-js library has 3 main objects that are used during all of the code samples. Here's an example of how to instantiate them:

import Web3 from "web3";
import { ChildChain, RootChain, OmgUtil } from "@omisego/omg-js";
const web3 = new Web3(new Web3.providers.HttpProvider(web3_provider_url));
const rootChain = new RootChain({ web3, plasmaContractAddress });
const childChain = new ChildChain({ watcherUrl });
const erc20ContractAddress = "0xd92e713d051c37ebb2561803a3b5fbabc4962431";
const aliceAddress = "0x8cb0de6206f459812525f2ba043b14155c2230c0";

• web3_provider_url - the URL to a full Ethereum RPC node (local or from infrastructure provider, e.g. Infura).

• plasmaContractAddress - CONTRACT_ADDRESS_PLASMA_FRAMEWORK for defined environment.

• watcherUrl - the Watcher Info URL for defined environment (personal or from OMG Network).

3. Retrieve balances

There's no direct way to retrieve balances on both Ethereum and OMG Network. Instead, you first retrieve an RLP encoded array of BigNum balances and then convert it to a preferred format.

The amount in balance array is defined in WEI (e.g. 429903000000000000), the smallest denomination of ether, ETH. The currency contains 0x0000000000000000000000000000000000000000 for ETH currency or a smart contract address (e.g. 0xd92e713d051c37ebb2561803a3b5fbabc4962431) for ERC20 tokens.

3.1 Retrieve child chain (OMG Network) balances

async function retrieveChildChainBalance() {
  
  const childchainBalanceArray = await childChain.getBalance(aliceAddress);
  
  const childchainBalance = childchainBalanceArray.map((i) => {
    return {
      currency:
        i.currency === OmgUtil.transaction.ETH_CURRENCY ? "ETH" : i.currency,
      amount:
        i.currency === OmgUtil.transaction.ETH_CURRENCY ?
          web3.utils.fromWei(String(i.amount), "ether") :
          web3.utils.toBN(i.amount).toString()
    };
  });

Note, the amount for ERC20 tokens will be displayed in the lowest denomination of that particular token. You can convert it into a number via web3.utils.fromWei. For example, the provided address has multiple tokens with different decimals (18, 0, 18, 18, 6):

[
  {
    "currency": "ETH",
    "amount": "0.299969999999999963"
  },
  {
    "currency": "0x2d453e2a14a00f4a26714a82abfc235c2b2094d5",
    "amount": "100"
  },
  {
    "currency": "0x5592ec0cfb4dbc12d3ab100b257153436a1f0fea",
    "amount": "100000000000000000000"
  },
  {
    "currency": "0x942f123b3587ede66193aa52cf2bf9264c564f87",
    "amount": "100000000000000000000"
  },
  {
    "currency": "0xd92e713d051c37ebb2561803a3b5fbabc4962431",
    "amount": "687000000"
  }
]

For example, if you want to convert the amount for TUSDT token (0xd92e713d051c37ebb2561803a3b5fbabc4962431), you should either create a custom converter or use the web3.utils as follows:

  web3.utils.fromWei(String(i.amount), "mwei")

You can find the number of decimals for a given token on one of the blockchain explorers, such as Etherscan.

3.2 Retrieve root chain (Ethereum) balances

async function retrieveRootChainErc20Balance() {
  
  const rootchainBalance = await web3.eth.getBalance(aliceAddress);
  const rootchainBalances = [
    {
      currency: "ETH",
      amount: web3.utils.fromWei(String(rootchainBalance), "ether"),
    },
  ];  
  const rootchainERC20Balance = await OmgUtil.getErc20Balance({
    web3,
    address: aliceAddress,
    erc20Address: erc20ContractAddress,
  });
  rootchainBalances.push({
    currency: erc20ContractAddress,
    amount: web3.utils.toBN(rootchainERC20Balance).toString(),
  });
}

Note, you can return the ERC20 balance only for one token at a time.