web3, truffle, nodejs error : UnhandledPromiseRejectionWarning - node.js

Question

var web3 = require('web3'),
contract = require('truffle-contract'),
path = require('path'),
MyContractJSON = require(path.join(__dirname, '../tru_dir/build/contracts/NewCoin.json'));
var provider = new web3.providers.HttpProvider("http://localhost:8545");
var MyContract = contract(MyContractJSON);
MyContract.setProvider(provider);
MyContract.deployed().then(function(instance){
return instance.returnfive();
})
.then(function(result) {
console.log(result);
}, function(error) {
console.log(error);
});
I set this code to call a smart contract function that returns 5.
I tested it with truffle console and it works properly.
But when trying to get the same result using nodejs it crashes giving those 2 errors :
(node:6227) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 2): TypeError: Cannot read property 'apply' of undefined
(node:6227) DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
Any idea about the issue ?

Answer 1

Replace MyContract definition with
const MyContract = artifacts.require("MyContractewCoin")
// You are missing this step before invoking deployer
await deployer.deploy(MyContract)
const dMyContract = await MyContract.deployed()
// now you can do stuff like
let result = await dMyContract.someContractFunction(args)