Something like this using jQuery?
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<select id = 'first'>
<option disabled selected>--select</option>
<option>ABC</option>
<option>123</option>
</select>
<select id = 'second' style="display:none">
</select>
<script>
var optionsAbc="<option>A</option><option>B</option>";
var options123 = '<option>1</option><option>2</option>';
$("#first").change(function() {
$("#second").show();
var value = $(this).val();
if(value == 'ABC') {
$("#second").html(optionsAbc);
} else if (value == '123') {
$("#second").html(options123);
}
});
</script>
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solved if selected abc in select element how happen abc group items in second select element [closed]