import { Validator } from "vee-validate"; const isBetween = (value, { min, max } = {}) => { return Number(min) <= value.length && Number(max) >= value.length; }; // The first param is called 'min', and the second is called 'max'. const paramNames = ['min', 'max']; Validator.extend('digits_between', isBetween, { paramNames // pass it in the extend options. });