JSFiddle - React, Tailwind, and code Playground

HTML

<input type="number" maxlength='6' name="pincode" id="pincode" size="30" max="999999" >

JavaScript

var pincode = document.getElementById('pincode');
var maxLength = pincode.maxLength;
pincode.onkeypress = function(e){
    if( pincode.value.length >= maxLength ){
        return false;
    }
};