Solidity, push overrides array

Question

pragma solidity 0.4.24;


contract ArraysExample {
   uint[] numbers;

   function addUser() public returns (uint[]) {
      numbers.push(random());
      return numbers;
   }

   function random() private view returns (uint8) {
      return uint8(uint256(keccak256(block.timestamp, block.difficulty))%251);
   }
}

When I call the following contracts method

const Web3 = require("web3");
const web3 = new Web3();
web3.setProvider(new 
web3.providers.HttpProvider("http://localhost:7545"));

const fs = require("fs");
const abi = JSON.parse(fs.readFileSync("abi.json", "utf8")).abi;
const contractAddress = "0x1fba6995e24ffa28bd0d14acd16e6f4cdac8df68";

const contractInstance = new web3.eth.Contract(abi, contractAddress);

contractInstance.methods
.addUser() 
.call()
.then(numbers => console.log(numbers));

I get this response when I execute the following code instead of ['142', '215', '8' ... ]:

score 1 · Accepted Answer · answered Nov 19 '18 at 17:50

1

The contract works.

Here it is Remix, returning an array with multiple items, as expected.

Your testing methodology is flawed. Specifically, you're using the .call() method which is a read-only invocation, like a dry run. It can't update the state. This is why the array isn't growing.

Have a look over here for a more complete explainer: https://blog.b9lab.com/calls-vs-transactions-in-ethereum-smart-contracts-62d6b17d0bc2

answered Nov 19 '18 at 17:50

Rob Hitchens

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1

Thank you Rob, that worked for me. I needed to add an event to my contract and emit it. web3.eth.getAccounts().then(accounts => { contractInstance.methods .addUser() .send({ from: accounts[0] }) .then(txReceipt => { console.log(txReceipt.events.newNumberPushed); }); }); it's how my code looks like now. – Marcello Bardus Nov 19 '18 at 20:51

Solidity, push overrides array

1 Answers1