POS client

import { POSClient,use } from "@maticnetwork/maticjs"
import { Web3ClientPlugin } from '@maticnetwork/maticjs-web3'
import HDWalletProvider from "@truffle/hdwallet-provider"

// install web3 plugin
use(Web3ClientPlugin);

const posClient = new POSClient();
await posClient.init({
    network: 'testnet',
    version: 'amoy',
    parent: {
      provider: new HDWalletProvider(privateKey, mainRPC),
      defaultConfig: {
        from : fromAddress
      }
    },
    child: {
      provider: new HDWalletProvider(privateKey, childRPC),
      defaultConfig: {
        from : fromAddress
      }
    }
});

const erc20ChildToken = posClient.erc20(<token address>);

const erc20ParentToken = posClient.erc20(<token address>, true);

const balance = await erc20ChildToken.getBalance(<userAddress>)
console.log('balance', balance)

// approve amount 10 on parent token
const approveResult = await erc20ParentToken.approve(10);

// get transaction hash
const txHash = await approveResult.getTransactionHash();

// get transaction receipt
const txReceipt = await approveResult.getReceipt();