upload_test.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <form id="myForm">
      <input type="file" id="csvFile" accept=".csv" />
      <br />
      <input type="submit" value="Submit" />
    </form>
    <script>
      const myForm = document.getElementById("myForm");
      const csvFile = document.getElementById("csvFile");
  
      myForm.addEventListener("submit", function (e) {
        e.preventDefault();
        const input = csvFile.files[0];
        const reader = new FileReader();
  
        reader.onload = function (e) {
          const text = e.target.result;
          document.write(text);
        };
  
        reader.readAsText(input);
      });
    </script>
  </body>
</html>