Multiple clients that need access to an async resource can share a single call via promises

shared-promise.js

// if several clients latch on to the same promise, do they all receive the results?

let thePromise = null;
const getSharedPromise = () => {

    // first time invocation, spin up the async activity
    // (connect to db, fetch crypto price quote, etc, etc)
    if(thePromise === null) {
        thePromise = new Promise((resolve, reject) => {
            setTimeout(() => {
                thePromise = null;
                resolve('something');
            }, 2500);
        });
    }

    // otherwise, return the current promise,
    // which will resolve to the same result for everyone
    return thePromise;
};

/**
 * output:
 *
client 1: something
client 2: something
client 3: something
 */
const client1 = getSharedPromise().then((r) => console.log(`client 1: ${r}`))
const client2 = getSharedPromise().then((r) => console.log(`client 2: ${r}`))
const client3 = getSharedPromise().then((r) => console.log(`client 3: ${r}`))