validate max input length

index.html

<div class="form-options"> 
  <input id="pincode" type="number" 
    onkeypress="validateNumberFields(event)" pattern="\d*"
    oninput="this.value=this.value.replace(/[^0-9]/g,'');" 
    type="number" 
    maxlength="6" />
</div>

script.js

function validateNumberFields(event) {

    $(`#${event.target.id}`).on("keyup", function (e) {

      var $field = $(this),
        val = this.value,
        $thisIndex = parseInt($field.data("idx"), 10);
      if (this.validity.badInput || isNaN(val) || $field.is(":invalid")) {


        // this.value = inputQuantity[$thisIndex];

        if (this.validity.badInput) {
          this.value = inputQuantity[$thisIndex];
        } else {
          this.value = ""
        }
        return;
      }

      if (val.length > Number($field.attr("maxlength"))) {

        val = val.slice(0, event.target.maxLength);

        $field.val(val);
      }
      // console.log(event.which)

      inputQuantity[$thisIndex] = val;
    });
  };