HTML Code
<!DOCTYPE html>

<html lang="en">

<head>

  <meta charset="UTF-8">

  <meta name="viewport" content="width=device-width, initial-scale=1.0">

  <title>onpopstate — SPA router</title>

  <style>

    body {

      font-family: system-ui, sans-serif;

      margin: 0;

      padding: 1.5rem;

      background: #f8fafc;

      color: #334155;

      line-height: 1.7;

    }

    h1 { margin: 0 0 0.75rem; font-size: 1.25rem; color: #0f172a; }

    nav { display: flex; gap: 0.5rem; flex-wrap: wrap; margin: 1rem 0; }

    nav a {

      padding: 0.5rem 1rem;

      border: 1px solid #cbd5e1;

      border-radius: 8px;

      background: #fff;

      text-decoration: none;

      color: #334155;

      font-size: 0.875rem;

    }

    nav a.is-active { background: #2563eb; border-color: #2563eb; color: #fff; }

    #view {

      padding: 1rem;

      background: #fff;

      border: 1px solid #e2e8f0;

      border-radius: 8px;

      max-width: 420px;

    }

    #view h2 { margin: 0 0 0.5rem; font-size: 1rem; color: #0f172a; }

  </style>

</head>

<body>

  <h1>Mini SPA with popstate</h1>

  <p>Click nav links, then use Back/Forward — the view syncs from event.state.</p>

  <nav>

    <a href="/c" data-route="c">C</a>

    <a href="/cpp" data-route="cpp">C++</a>

    <a href="/java" data-route="java">Java</a>

  </nav>

  <div id="view"><h2>C</h2><p>Learn C programming on CodeToFun.</p></div>



  <script>

    var views = {

      c: "<h2>C</h2><p>Learn C programming on CodeToFun.</p>",

      cpp: "<h2>C++</h2><p>Explore C++ tutorials and examples.</p>",

      java: "<h2>Java</h2><p>Browse Java programming lessons.</p>"

    };



    function render(route) {

      document.getElementById("view").innerHTML = views[route] || views.c;

      document.querySelectorAll("nav a").forEach(function (link) {

        link.classList.toggle("is-active", link.dataset.route === route);

      });

    }



    document.querySelector("nav").addEventListener("click", function (event) {

      var link = event.target.closest("a[data-route]");

      if (!link) return;

      event.preventDefault();

      var route = link.dataset.route;

      history.pushState({ route: route }, "", link.getAttribute("href"));

      render(route);

    });



    window.addEventListener("popstate", function (event) {

      var route = (event.state && event.state.route) ? event.state.route : "c";

      render(route);

    });



    history.replaceState({ route: "c" }, "", "/c");

    render("c");

  </script>

</body>

</html>
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HTML onpopstate Attribute — SPA router with event.state
