Async tasks checker

async-tasks-checker.js

class Foo {
    constructor(time, answer) {
        this._time = time;
        this._answer = answer;
    }
    get time() {
        return this._time;
    }
    is() {
        return new Promise(res => setTimeout(() => res(this._answer), this._time));
    }
}

async function find(items) {
    let counter = items.length;
    if (!counter) return null;
    const result = new Promise(res => {
        items.forEach(
            item => {
                item.is().then(isCompleted => {
                    if(isCompleted) return res(item);
                    if (--counter === 0) res(null);
                })
            }
        );
    });
    return await result;
}



async function filter(items) {
    const newItems = [];
    let counter = items.length;
    if (!counter) return newItems;
     const result = new Promise(res => {
        items.forEach(
            item => {
                item.is().then(isCompleted => {
                    if(isCompleted) newItems.push(item);
                    if (--counter === 0) res(newItems);
                })
            }
        );
    });
    return await result;
}

// Tests
{
    (async function() {
        const foos = [new Foo(1000, true), new Foo(123, false), new Foo(125, true), new Foo(2349, false)];
        const value = await find(foos);
        console.assert(value.time === 125, 'Find -> positive case failed');
    }());
}
{
     (async function() {
        const foos = [new Foo(1000, false), new Foo(123, false), new Foo(125, false), new Foo(2349, false)];
        const value = await find(foos);
        console.assert(value === null, 'Find -> edge case failed');
    }());
}
{
     (async function() {
        const foos = [new Foo(1000, true), new Foo(123, false), new Foo(125, true), new Foo(2349, false)];
        const values = await filter(foos);
        const expected = [foos[2], foos[0]];
        expected.forEach((item, index) => console.assert(item === values[index], 'Filter -> positive case failed'));
    }());
}
{
     (async function() {
        const foos = [new Foo(1000, false), new Foo(123, false), new Foo(125, false), new Foo(2349, false)];
        console.time('perf');
        const values = await filter(foos);
        console.timeEnd('perf');
        console.assert(values.length === 0, 'Filter -> edge case failed');
    }());
}