HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>(ha)*</title>
</head>
<body>
  <h1>Repeated group</h1>
  <pre id="out"></pre>
  <script>
    var laughs = ["", "ha", "haha", "hahaha", "ho"];
    document.getElementById("out").textContent = laughs.map(function (s) {
      return JSON.stringify(s) + " → " + /^(ha)*$/.test(s);
    }).join("\n");
  </script>
</body>
</html>

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JavaScript RegExp * quantifier — (ha)* group (Try It)