GST Number Client Side verification

html

<link href="https://fonts.googleapis.com/css?family=Raleway:300,400,600" rel="stylesheet" type="text/css">
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<div class="container">
    <div class="row justify-content-center">
        <div class="col-md-12">
            <div class="card">
                <div class="card-header">New Vendor Add</div>
                <div class="card-body">

                    <form autocomplete="off" >
                        <div class="form-group">
                          <label for="gstno">GST Number</label>
                          <input type="text" class="form-control" id="gstno" aria-describedby="gstno" placeholder="Enter GST number" style="text-transform:uppercase" maxlength="15" >
                          <small id="gstnoHelp" class="form-text"></small>
                        </div>
                        <button id="verify" class="btn btn-primary">Verify</button>
                      </form>
                </div>
            </div>
        </div>
    </div>
</div>



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<script type="text/javascript">
$(document).ready(function() {

var gstn = $("#gstno");





$("#gstno").keyup(function(){
    console.log(gstn.val().length);
    if (gstn.val().length < 15) {
        // console.log("les than 15");
        gstninvalid(); 
    } else if (gstn.val().length > 15) {
        console.log("greather 15")
        gstnover()
    } else {
        var word = $("#gstno").val();
        var test = word.slice(0,2);
        city(test);
        // gstnvalid()
    }
});


function gstninvalid() {
    $("#gstnoHelp").addClass("text-danger");
    $("#gstno").addClass("is-invalid");
    $("#gstnoHelp").html("Please Input Valid GSTN");
}

function gstnvalid(citycode) {
    $("#gstnoHelp").addClass("text-success");
    $("#gstno").addClass("is-valid");
    $("#gstno").removeClass("is-invalid");
    $("#gstnoHelp").removeClass("text-danger");
    $("#gstnoHelp").html("GSTN Valid for " + citycode);
}

function gstnover() {
    $("#gstnoHelp").removeClass("text-success");
    $("#gstnoHelp").addClass("text-danger");
    $("#gstno").removeClass("is-valid");
    $("#gstno").addClass("is-invalid");
    $("#gstnoHelp").html("GSTN not Over Than 15 Charecter");
    // alert('check GSTN');
}


function city(test) {
    iNum = parseInt(test)
    switch(iNum) {
    case 01:
        var citycode = "Jammu and Kashmir";
        gstnvalid(citycode);
        break;
    case 02:
        var citycode = "Himachal Pradesh";
        gstnvalid(citycode);
        break;
    case 03:
        var citycode = "Punjab";
        gstnvalid(citycode);
        break;
    case 04:
        var citycode = "Chandigarh";
        gstnvalid(citycode);
        break;
    case 05:
        var citycode = "Uttranchal";
        gstnvalid(citycode);
        break;
    case 06:
        var citycode = "Haryana";
        gstnvalid(citycode);
        break;
    case 07:
        var citycode = "Delhi";
        gstnvalid(citycode);
        break;
    case 08:
        var citycode = "Rajasthan";
        gstnvalid(citycode);
        break;
    case 09:
        var citycode = "Uttar Pradesh";
        gstnvalid(citycode);
        break;
    case 10:
        var citycode = "Bihar";
        gstnvalid(citycode);
        break;
    case 11:
        var citycode = "Sikkim";
        gstnvalid(citycode);
        break;
    case 12:
        var citycode = "Arunachal Pradesh";
        gstnvalid(citycode);
        break;
    case 13:
        var citycode = "Nagaland";
        gstnvalid(citycode);
        break;
    case 14:
        var citycode = "Manipur";
        gstnvalid(citycode);
        break;
    case 15:
        var citycode = "Mizoram";
        gstnvalid(citycode);
        break;
    case 16:
        var citycode = "Tripura";
        gstnvalid(citycode);
        break;
    case 17:
        var citycode = "Meghalaya";
        gstnvalid(citycode);
        break;
    case 18:
        var citycode = "Assam";
        gstnvalid(citycode);
        break;
    case 19:
        var citycode = "West Bengal";
        gstnvalid(citycode);
        break;
    case 20:
        var citycode = "Jharkhand";
        gstnvalid(citycode);
        break;
    case 21:
        var citycode = "Orissa";
        gstnvalid(citycode);
        break;
    case 22:
        var citycode = "Chhattisgarh";
        gstnvalid(citycode);
        break;
    case 23:
        var citycode = "Madhya Pradesh";
        gstnvalid(citycode);
        break;
    case 24:
        var citycode = "Gujarat";
        gstnvalid(citycode);
        break;
    case 25:
        var citycode = "Daman and Diu";
        gstnvalid(citycode);
        break;
    case 26:
        var citycode = "Dadra and Nagar Haveli";
        gstnvalid(citycode);
        break;
    case 27:
        var citycode = "Maharashtra";
        gstnvalid(citycode);
        break;
    case 28:
        var citycode = "Andhra Pradesh";
        gstnvalid(citycode);
        break;
    case 29:
        var citycode = "Karnataka";
        gstnvalid(citycode);
        break;
    case 30:
        var citycode = "Goa";
        gstnvalid(citycode);
        break;
    case 31:
        var citycode = "Lakshdweep";
        gstnvalid(citycode);
        break;
    case 32:
        var citycode = "Kerala";
        gstnvalid(citycode);
        break;
    case 33:
        var citycode = "Tamil Nadu";
        gstnvalid(citycode);
        break;
    case 34:
        var citycode = "Pondicherry";
        gstnvalid(citycode);
        break;
    case 35:
        var citycode = "Andaman and Nicobar Islands";
        gstnvalid(citycode);
        break;
    default:
        gstninvalid()
        break;
} 
}

$("#verify").click(function( event ){
    event.preventDefault();
    
    console.log(gstn.val().length);
    

});

} );
</script>