Custom validation in Lightning web component

customValidation.html

=====================

<template>

<lightning-input type="text" label="FirstName" class="FName" onchange={handleChange}>

</lightning-input>

<lightning-input type="checkbox" label="Choose" class="Choose" onchange={handleChange}>

</lightning-input>

</template>

customValidation.js

===================

import { LightningElement, track } from 'lwc';

export default class CustomValidation extends LightningElement {

handleChange(event){

    let currentLabel=event.target.label;

    console.log('@@@@label@@'+currentLabel);

    if(currentLabel==="FirstName"){

        let fname=this.template.querySelector(".FName");

        let fnameval=fname.value;

        if(! fnameval){

            fname.setCustomValidity("Please Enter the FirstName");

        }

        else{

            fname.setCustomValidity("");

        }

        fname.reportValidity();

    }

    else if(currentLabel==="Choose"){

        let isChecked=this.template.querySelector(".Choose");

        let isCheckedVal=isChecked.checked;

        if(isCheckedVal==false){

            isChecked.setCustomValidity("Please tick the checkbox");

        }

        else{

            isChecked.setCustomValidity("");

        }

        isChecked.reportValidity();

    }

}

}