how to show another dropdown box depend on dropdown box value - php

Question

please i need help
i need to do specail command
when some value selected then show another dropdown box
my first dropdown box is in php
and he is my code :
$conn = mysqli_connect("localhost", "root",
"", "phoneunlock" )
or die("Cannot connect to database:" .
mysqli_connect_error($conn));
echo "<select name='selectedValue' class= 'dropdown' >";
echo '<option value="">'.'Please Select Service'.'</option>';
$sql = "SELECT id, manufacter FROM product";
$result = $conn->query($sql);
while($row = $result->fetch_assoc())
{ echo "<option value='" . $row['manufacter']. "'>" . $row['manufacter'] . '</option>';
}
echo '</select>';
and know i need some command like this :
if dropdown box selected = value then
do this
end if
sow please can any one help me

Answer 1

if you mean like chained combobox. try using jQuery like this :
$('#yourcomboid').on('change', function() {
var id = $(this).val();
$('#youranothercombo').empty();
$.ajax({
url: 'your-route-to-get-data/' + id,
success: function(data) {
$('#youranothercombo').empty();
for(var i = 0; i < data.length; i++) {
var item = data[i];
$('#youranothercombo').append($('<option></option>').val(item.column-name).text(item.column-name));
}
}
});
});
Hope this code works.