<form class='wrapper' name='myforma'>
  <label for='text1'>
      <input type='number' id='text1' placeholder='Text'>
  </label>
  <label for='text2'>
      <input type='number' id='text2' placeholder='Text'>
  </label>
    <label for='text3'>
      <input type='number' id='text3' placeholder='Text'>
  </label>
  <button type='submit'>Touch me</button>
</form>

label {
  display: block;
  margin-bottom: 15px;
}

const url = "site.ru";

document.querySelector("#text2").addEventListener("keyup", e => {
  fetch(url, {
    method: "POST",
    headers: {
      "Content-Type": "application/x-www-form-urlencoded"
    },
    body: e.target.value
  })
    .then(response => response.text())
    .then(result => console.log(result))
    .catch(error => console.log("error", error))
})