- index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="script.js"></script>
</head>
<body>
    <div>
        <p>
            Від:
            <input type="number" value="1" min="1" id="min" />
            До:
            <input type="number" value="100" min='2' id="max" />
        </p>
        <p>
            <button id="searchButton" onclick="searchNums()">Search</button>
        </p>
        <div>
            <div id="status"></div>
            <div id="result"></div>
        </div>
    </div>
</body>
</html>

- script.js

function searchNums() {
    let statusDisplay = document.getElementById("status");
    let searchButton = document.getElementById("searchButton");
    searchButton.disabled = true;

    let min = document.getElementById('min').value;
    let max = document.getElementById('max').value;

    let worker = new Worker("NumWorker.js");

    statusDisplay.innerHTML = 'Searching...';

    worker.onmessage = receivedWorkerMessage;

    worker.postMessage(
        { from: min,
            to: max
        }
    );
}

- NumWorker.js

function findNums(min, max) {
    let list = [];
    for (let i=min; i<=max; i++) {
        if (i>1) list.push(i);
    }

    let maxDiv = Math.round(Math.sqrt(max));
    let nums = [];

    for (let i=0; i<list.length; i++) {
        let failed = false;
        for (let j=2; j<=maxDiv; j++) {
            if ((list[i] != j) && (list[i] % j == 0)) {
                failed = true;
            } else if ((j==maxDiv) && (failed == false)) {
                nums.push(list[i]);
            }
        }
    }

    return nums;
}

onmessage = function(event) {
    let nums = findNums(event.data.from, event.data.to);

    postMessage(nums);
};

function receivedWorkerMessage(event) {
    let primes = event.data;

    let primeList = "";
    for (let i=0; i<primes.length; i++) {
        primeList += primes[i];
        if (i !== primes.length-1) primeList += ", ";
    }

    let primeContainer = document.getElementById("result");
    primeContainer.innerHTML = primeList;

    let statusDisplay = document.getElementById("status");

    let searchButton = document.getElementById("searchButton");

    if (primeList.length == 0) {
        statusDisplay.innerHTML = "Error!";
    }
    else {
        statusDisplay.innerHTML = "Done!";
    }

    searchButton.disabled = false;
}