const abi = fs.readFileSync('erc20_abi.json', 'utf-8');
const contract = new web3.eth.Contract(JSON.parse(abi), contract_address)

contract.methods.balanceOf(address).call().then(console.log).catch(console.error);
contract.methods.transfer(to_address, amount).send().then(console.log).catch(console.error);