clock1.js

// A Promise-based wrapper around setTimeout() that we can use await with.
// Returns a Promise that fulfills in the specified number of milliseconds
function elapsedTime(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}

// An async generator function that increments a counter and yields it
// a specified (or infinite) number of times at a specified interval.
async function* clock(interval, max=Infinity) {
    for(let count = 1; count <= max; count++) { // regular for loop
        await elapsedTime(interval);            // wait for time to pass
        yield count;                            // yield the counter
    }
}

// A test function that uses the async generator with for/await
async function test() {                       // Async so we can use for/await
    for await (let tick of clock(300, 100)) { // Loop 100 times every 300ms
        console.log(tick);
    }
}