title: How to auto add slash(/) in expiry date field input javascript
body: <p>I wanna auto add slash in credit card expiry date field input. I wanna add slash after type 2 character and remove slash after delete third digit. Example, 23/ (auto add slash after type number 3) 23/4 (auto remove slash after delete number 4)</p>
  <pre><code>addSlashes(elementID) {
      let ele = document.getElementById(elementID)
      const value = ele.value
      let finalVal = null
      if (value.length === 2) {
         finalVal = `${value}/`
      }
      document.getElementById(elementID).value = finalVal
  },
  </code></pre>