requestIdle.js

let refCount = 0;
let resolvers = [];

function resolveAll() {

    for (let resolve of resolvers)
        resolve();

    resolvers = [];

}

function checkRefCount() {

    if (refCount > 0)
        return ;

    resolveAll();

}

function checkBrowserIdle() {

    if (window.requestIdleCallback) {
        window.requestIdleCallback(checkRefCount);
    } else {
        window.setTimeout(checkRefCount, 0);
    }

}

export async function requestIdle() {

    return new Promise(resolve => {

        resolvers.push(resolve);

        checkBrowserIdle();

    });

}

requestIdle.increaseRefCount = () => {

    refCount += 1;

};

requestIdle.decreaseRefCount = () => {

    refCount -= 1;

    checkBrowserIdle();

};