Lesson 9: Why the async function is executed immediately and why it takes few seconds after event is emitted until the listener is executed

[software-dev2010]

Hello, I'm not an expert in JavaScript and I want to ask you why the async function is executed immediately. This Promise has a parameter that is an async function, and from what I know an async function isn't executed immediately, it is executed when it is called, not when it is declared, but in this case I see that it is executed immediately. I don't understand why it is executed immediately.

    it("picks a winner, resets, and sends money", async () => {
        ...
        await new Promise(async (resolve, reject) => {
            raffle.once("WinnerPicked", async () => {
                console.log("Found the event!");
                try {
                    ...
                } catch (e) {
                    reject(e);
                }
                resolve();
            });
            ...
            await vrfCoordinatorV2Mock.fulfillRandomWords(
                txReceipt.events[1].args.requestId, 
                raffle.address);
            console.log("LOG-5");
        });

In the hardhat.config.js is configured a timeout for listener. I didn't understand very well how the listener knows about this field timeout.

module.exports = {
...
  mocha: {
    timeout: 200000, // 200 seconds
  }
}; 

And another question is why it takes a couple of seconds after the event is emitted until the listener is executed.
raffle.once("WinnerPicked", async () => {...}); - here it'll wait for the WinnerPicked event to be emitted, and at that moment the async function which represents a listener will be executed. And the waiting time is set in the hardhat.config.js file. When this function vrfCoordinatorV2Mock.fulfillRandomWords() is called, the event is emitted but I tested it and I see that it take few seconds until the listener is executed. Thank you!

[alymurtazamemon]

@software-dev2010 You must be working on a local network due to that it is fast. And how it knows about the timeout so it is all configurations by hardhat. And why it takes seconds after fulfillRandomWords call so first it completes this call;

await vrfCoordinatorV2Mock.fulfillRandomWords(
  txReceipt.events[1].args.requestId, 
  raffle.address
);

then smart contract's emit event so it gove here;

raffle.once("WinnerPicked", async () => {
    console.log("Found the event!");
    try {
        ...
    } catch (e) {
        reject(e);
    }
    resolve();
});

and then it resolve the promise so all of this execution takes these seconds.