JSFiddle - React, Tailwind, and code Playground

HTML

<div class="plan">
    <div class="plan-details1"></div>
    <div class="plan-name">
        <select id="myselect">
            <option value="0">Please Select Your Mobile Plan</option>
            <option value="1">Package 1</option>
            <option value="2">Package 2</option>
            <option value="3">Package 3</option>
            <option value="4">Package 4</option>
            <option value="5">Package 5</option>
            <option value="6">Package 6</option>
        </select>
    </div>
    <div class="plan-price"></div>
</div>

JavaScript

$(function () {
    $('#myselect').change(function () {
        var val = $(this).val();

        if (val == '1') {
            $('.plan-details1').html('This Is Working 1<br/>');
            $('.plan-price').html('<div id="price-m">Price: &euro;18</div><input type="checkbox" id="handset-m" value="Car"> Handset');
            document.getElementById("handset-m").onclick = validate;
        }

        if (val == '2') {
            $('.plan-details1').html('This Is Working 2<br/>');
            $('.plan-price').html('<div id="price-l">Price: &euro;25</div><input type="checkbox" id="handset-l" value="Car"> Handset');
            document.getElementById("handset-l").onclick = validate;
        }

        if (val == '3') {
            $('.plan-details1').html('This Is Working 3<br/>');
        }

        if (val == '4') {
            $('.plan-details1').html('This Is Working 4<br/>');
        }

        if (val == '5') {
            $('.plan-details1').html('This Is Working 5<br/>');
        }

        if (val == '6') {
            $('.plan-details').html('This Is Working 6<br/>');
        }

    });
});

function validate() {
    if (document.getElementById('handset-m')) {
        if (document.getElementById('handset-m').checked) {
            document.getElementById('price-m').innerHTML = 'Price: &euro;20';
        } else {
            document.getElementById('price-m').innerHTML = 'Price: &euro;18';
        }
    }
    if (document.getElementById('handset-l')) {
        if (document.getElementById('handset-l').checked) {
            document.getElementById('price-l').innerHTML = 'Price: &euro;35';
        } else {
            document.getElementById('price-l').innerHTML = 'Price: &euro;25';
        }
    }
}