function doUntil(loop, stopCondition, yieldCondition) {

    // Wrap function in promise so it can run asynchronously
    return new Promise((resolve, reject) => {

	// Build outerLoop function to pass to setTimeout
	let outerLoop = function () {
	    while (true) {
		
		// Execute a single inner loop iteration
		loop();

		if (stopCondition()) {
		    // Resolve promise, exit outer loop, and do not re-enter
		    resolve();
		    break;
		} else if (yieldCondition()) {
		    // Exit outer loop and queue up next outer loop iteration
		    // for next event cycle
		    setTimeout(outerLoop, 0);
		    break;
		}
		
		// Continue to next inner loop iteration without yielding
	    }
	};

	// Start the first iteration of outer loop, unless the stop condition is met 
	if (!stopCondition()) {
	    setTimeout(outerLoop, 0);
	}
    });
}

// Check whether n is prime, given a list of all primes < n
function isPrime(n, primes) {
    for (const p of primes) {
	if (n % p == 0) {
	    return false;
	}
    }
    return true;
}

function findPrimesBlocking() {
    let primes = [];

    for (let n = 2; n < 1000000; n++) {
	if (isPrime(n, primes)) {
	    primes.push(n);
	}
	if (n % 10000 == 0) {
	    let status = `Found ${primes.length} primes between 2 and ${n}`;
	    document.getElementById("display").textContent = status;
	    console.log(status);
	}
    }
    document.getElementById("display").textContent =
	`Found ${primes.length} primes between 2 and 1000000`;
}

function findPrimesNonBlocking() {

    // Initialize loop variable and list of primes
    let n = 2;
    let primes = [];

    // Yield every 1000 iterations and stop after 1000000
    const stopCondition = () => n == 1000000;
    const yieldCondition = () => n % 10000 == 0;

    // Build the loop body to be passed to doUntil()
    const loop = () => {

	// Determine if n is prime
	if (isPrime(n, primes)) {
	    primes.push(n);
	}

	// Increment n
	n += 1;

	// Update DOM if we're about to yield
	if (yieldCondition()) {
	    let status = `Found ${primes.length} primes between 2 and ${n}`;
	    document.getElementById("display").textContent = status;
	    console.log(status);
	}
    };

    // Execute
    doUntil(loop, stopCondition, yieldCondition);
}