JSFiddle - React, Tailwind, and code Playground

HTML

<input type='text' id='input' />
<button id='btn' disabled>
Button
</button>

JavaScript

let val = function() {
  let input = document.querySelector('#input');
  let button = document.querySelector('#btn');
  if (input.value.length >= 7 && input.value.length <= 10) {
    button.disabled = false;
  } else button.disabled = true;
}

document.getElementById('input').addEventListener('input', val)