During my investigation, I would like a piece of advice, please.

I am trying to get a random number generated by the VRF of the oracle chainlink from the front coded in ReactJS. I would like to get the random number thanks to an event event GenerateRandomResult.

here's the function needed implemented in a smart contract of my application:

contract X is AccessControl, VRFConsumerBase {

bytes32 internal keyHash;
    uint256 internal fee;
    uint256 public randomResult;

    event GenerateRandomResult(uint256 ramdomNumber);

    constructor(address pawnToken_address)
            0x8C7382F9D8f56b33781fE506E897a4F1e2d17255, // VRF Coordinator
            0x326C977E6efc84E512bB9C30f76E30c160eD06FB  // LINK Token

        keyHash = 0x6e75b569a01ef56d18cab6a8e71e6600d6ce853834d4a5748b720d06f878b3a4;
        fee = 0.0001 * 10 ** 18; // 0.1 LINK (Varies by network)

     * @notice Requests randomness
     * @return requestId the id of the request for the oracle
    function getRandomNumber() public returns (bytes32 requestId) {
        require(LINK.balanceOf(address(this)) >= fee, "Not enough LINK - fill contract with faucet");
        return requestRandomness(keyHash, fee);

     * @notice Callback function used by VRF Coordinator
     * @param requestId the id of the request for the oracle
     * @param randomness randomness must be requested from an oracle, which generates a number and a cryptographic proof
    function fulfillRandomness(bytes32 requestId, uint256 randomness) internal override {
        randomResult = randomness % 6 + 1;

        emit GenerateRandomResult(randomResult);

Can you tell me if the event/emit is well positioned in my smart contract?

When I test with remix these functions, everything works fine!

Of course, I "feed" the deployed contract with LINK of my Metamask wallet to run it on Polygon framework.

Now, to connect the front (I use Ether.js) & use the previous event event GenerateRandomResult in ReactJS with the back in Solidity, I try to use this:

 async function rollDiceFunction() {
    if (BoardSC == null) return;

    //TODO: Replace by the call at the oracle

    BoardSC.on("GenerateRandomResult", (ramdomNumber) => {
        console.log('ramdomNumber: ', ramdomNumber);

where BoardSC is an instance of my smart contract MonopolyBoard.sol but it doesn't work. I'll try to use this writing now:

 filter = {
        topics: [
            // the name of the event, parnetheses containing the data type of each event, no spaces
    provider.on(filter, () => {
        // do whatever you want here
        // I'm pretty sure this returns a promise, so don't forget to resolve it

Have you got any clue to suggest me to continue my developments?

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.