Trigger AJAX function on form loaded from mysql/php - php

Question

I have a drop down menu that is populated from a mysql table via php. When an item is selected a second drop down menu is triggered using a variable from the first form. This works as expected when making a selection via onchange trigger.
I would like to change this though, and have the script fire when the drop down is loaded and the selected item (set from previous page) is pre-set, I dont want any user interaction.
Here is the form code
<div><select class="form-control m-b" name="id" onChange="get_engineers(this.value)" style="font-family: monospace">
<?php
$qry = "SELECT id,name FROM products WHERE Parent_team = $parent_team ORDER BY name" ;
$stmt = $mysqli->prepare($qry);
$stmt->execute();
$result = $stmt->get_result();
while($row = $result->fetch_assoc()) {
if($product==$row['name']){
$selectCurrent='selected';
}else{
$selectCurrent='';}
echo '<option value="'.$row['id'].'" '.$selectCurrent.'>'.$row['name'].'</option>';
}
?>
</select>
</div>
</div>
And the second form drop down
<div class="form-group"><label class="control-label">Engineer</label>
<select class="form-control m-b" name="engineer" id="engineer" style="font-family: monospace">
<option selected="selected">--Select Engineer--</option>
</select>
</div>
And the script
<script>
function get_engineers(id)
{
$.ajax({
type: "GET",
url: "ajax_engineers.php", /* The engineer id will be sent to this file */
beforeSend: function () {
$("#engineer").html("<option>Loading ...</option>");
},
data: "id="+id,
success: function(msg){
$("#engineer").html(msg);
}
});
}
</script>
I tried onload instead of onchange but nothing happens.
thanks

Answer 1

First, add an id attribute to your first select:
<select id="my-unique-id" class="form-control m-b" name="id">
Then you can trigger it via the jQuery onload like so:
<script>
$(function(){
// This will run it on page load to catch any auto-filled values
get_engineers($('#my-unique-id').val());
// This will run it when the value is changed
$('#my-unique-id').change(function(){
get_engineers($(this).val());
});
});
</script>