These are example best practices for using Chainlink VRF.

Getting a random number within a range

If you need to generate a random number within a given range, use modulo to define the limits of your range. Below you can see how to get a random number in a range from 1 to 50.

function fulfillRandomWords(
  uint256, /* requestId */
  uint256[] memory randomWords
) internal override {
  // Assuming only one random word was requested.
  s_randomRange = (randomWords[0] % 50) + 1;
}

Getting multiple random values

If you want to get multiple random values from a single VRF request, you can request this directly with the numWords argument. See the Get a Random Number guide for an example where one request returns multiple random values.

Processing simultaneous VRF requests

If you want to have multiple VRF requests processing simultaneously, create a mapping between requestId and the response. You might also create a mapping between the requestId and the address of the requester to track which address made each request.

mapping(uint256 => uint256[]) public s_requestIdToRandomWords;
mapping(uint256 => address) public s_requestIdToAddress;
uint256 public s_requestId;

function requestRandomWords() external onlyOwner returns (uint256) {
  uint256 requestId = COORDINATOR.requestRandomWords(
    keyHash,
    s_subscriptionId,
    requestConfirmations,
    callbackGasLimit,
    numWords
  );
  s_requestIdToAddress[requestId] = msg.sender;

  // Store the latest requestId for this example.
  s_requestId = requestId;

  // Return the requestId to the requester.
  return requestId;
}

function fulfillRandomWords(
    uint256 requestId,
    uint256[] memory randomWords
  ) internal override {
  // You can return the value to the requester,
  // but this example simply stores it.
  s_requestIdToRandomWords[requestId] = randomWords;
}

You could also map the requestId to an index to keep track of the order in which a request was made.

mapping(uint256 => uint256) s_requestIdToRequestIndex;
mapping(uint256 => uint256[]) public s_requestIndexToRandomWords;
uint256 public requestCounter;

function requestRandomWords() external onlyOwner {
  uint256 requestId = COORDINATOR.requestRandomWords(
    keyHash,
    s_subscriptionId,
    requestConfirmations,
    callbackGasLimit,
    numWords
  );
  s_requestIdToRequestIndex[requestId] = requestCounter;
  requestCounter += 1;
}

function fulfillRandomWords(
    uint256 requestId,
    uint256[] memory randomWords
  ) internal override {
  uint256 requestNumber = s_requestIdToRequestIndex[requestId];
  s_requestIndexToRandomWords[requestNumber] = randomWords;
}