Server-side hot reload checker by Michael Kennedy. When the contents of the page change in any way, the page will be reloaded.

server-hot-reload.js

// *************************************************************************
// Server-side hot reload check by Michael Kennedy (https://mkennedy.codes).
// Released under the MIT open source license, 2023.
//
// Usage: Include this file in your "application shell" layout template
// or directly into any page you'd like to check.
//
// Set the checkIntervalInMs time to the frequency you need. Usually 1 sec
// should be fine, but if a page is slow maybe increase the delay.
//
// When the contents of the page change in any way, the page will be reloaded.
//

let currentPageHash = "UNKNOWN";
let checkIntervalInMs = 1000;
let setIntervalInstance;

// *************************************************************************
// When the doc is ready, we'll start checking for changes.
//
document.addEventListener("DOMContentLoaded", function () {
    console.log("Server hot reload active at " + new Date().toLocaleTimeString() + ". Watching for changes ...");
    const url = document.location.href;

    setIntervalInstance = setInterval(() => downloadHtml(url).then(reloadIfNecessary), checkIntervalInMs);
});

// *************************************************************************
// Called on every page content check (interval is checkIntervalInMs milliseconds).
//
function reloadIfNecessary(html) {
    const newHash = hashCode(html);
    if(!newHash) return;
    if (currentPageHash === "UNKNOWN") {
        // Compute the hash since have never seen this response on this URL before (first run).
        currentPageHash = newHash;
        return;
    }

    if (newHash === currentPageHash) {
        return;
    }

    // Something, somewhere in the page has changed. Reload
    console.log("Page change detected, reloading now!")
    window.location.reload();
}

function hashcode (html) {
    let hash = 0, i, chr;
    if (html.length === 0) return hash;
    for (i = 0; i < html.length; i++) {
        chr = html.charCodeAt(i);
        hash = ((hash << 5) - hash) + chr;
        hash |= 0; // Convert to 32bit integer
    }
    return hash;
}

async function downloadHtml(url) {
    const thisURL = new URL(url) 
    thisURL.searchParams.append('server_hot_reload_check=true')
    try{
        const request = await fetch(thisURL);
        return request.text();
    } catch (e) {
        console.log("Something went wrong. Stopping hot reload.")
        clearInterval(setIntervalInstance);
        return '';
    }
}