How to get solidity function return

Question

I have a contract called tracking. It has a function called move() I called this function using code:

import {bonds} from 'oo7-parity';
const counterABI = [...]
const ContractAddress = '...'

constructor() {
    super()
    this.counter = bonds.makeContract(ContractAddress, counterABI)
}


/*hidden code*/

this.counter.move(data, this.state.caminho[this.state.caminho.length - 1], id)

This function move() returns true or false. But how can I have access to this returned value?

I tried the following:

let res = this.counter.move(data, this.state.caminho[this.state.caminho.length - 1], id)
console.log(res)

But is doesn't work. This just print a huge json and I don't know where ir the returned value (true or false)

Answer 1

You probably want to do this using events. So in your contract you'll add something like this to the top of the contract.

event Minted(uint256 amount, uint256 totalCost);

and in your method you'll emit the event like this:

function mint(uint256 numTokens) public payable {
    uint256 priceForTokens = priceToMint(numTokens);
    require(msg.value >= priceForTokens);

    totalSupply = totalSupply.add(numTokens);
    balances[msg.sender] = balances[msg.sender].add(numTokens);
    poolBalance = poolBalance.add(priceForTokens);
    if (msg.value > priceForTokens) {
        msg.sender.transfer(msg.value - priceForTokens);
    }

    emit Minted(numTokens, priceForTokens);
}

Then in your Node.js code, you can iterate through the events with the .getPastEvents() method:

   await EthPolynomialCurveToken.getPastEvents(['Minted', 'Burned'], {fromBlock: blockNum, toBlock: 'latest'}, async (err, events) => {
      for(var i = 0; i < events.length(); i++){
        // Something like tokensMinted = events[i].returnValues.amount;
      } 
    })

If you want the most recent event you can just do something like:

events[events.length()].returnValues.amount