jquery $.post function is not executing the function - php

Question

I am trying to post data to populate my HTML dropdowns using jQuery's $.post as shown below.
var county = $("#county");
var constituency = $("#constituency");
var ward = $("#ward");
populate_fields();
$('select[name="political"]').change(function(ev) {
ev.preventDefault();
populate_fields();
});
function populate_fields() {
// call the server side script, and on completion, update all dropdown lists with the received values.
county.html('').append($('<option>').text('Please choose a county'));
constituency.html('').append($('<option>').text('Please choose a constituency'));
ward.html('').append($('<option>').text('Please choose a ward'));
var data = {
// pass all the currently selected values to the server side script.
"county" : county.val(),
"constituency" : constituency.val(),
"ward" : ward.val()
}
$.post('php/dropdown.php', data, function (resp) {
console.log('function works');
all_values = resp;
$.each(all_values.county, function () {
$option = $("<option>").text(this).val(this);
if (all_values.current_county == this) {
$option.attr('selected', 'selected');
}
county.append($option);
});
$.each(all_values.constituency, function () {
$option = $("<option>").text(this).val(this);
if (all_values.current_constituency == this) {
$option.attr('selected', 'selected');
}
constituency.append($option);
});
$.each(all_values.ward, function () {
$option = $("<option>").text(this).val(this);
if (all_values.current_ward == this) {
$option.attr('selected', 'selected');
}
ward.append($option);
});
},'json');
}
the php file being referred to works perfectly, however the post does not receive data from this file and the function does not execute, I have traced the problem to the above snippet of code. Anyone have an Idea as to what could be the problem?
Here is my php Code as requested for more insight into the problem:
<?php
// read the CSV file in the $makes_models_years array
$makes_models_years = array();
//$uploads_folder = wp_upload_dir()['basedir'];
$file = fopen("./resources/polling_data.csv","r");
$firstline = true;
while (($line = fgetcsv($file)) !== FALSE) {
if ($firstline) {
$firstline = false;
continue;
}
$makes_models_years[$line[0]][$line[1]][] = $line[2];
}
fclose($file);
// setup the initial array that will be returned to the the client side script as a JSON object.
$return_array = array(
'county' => array_keys($makes_models_years),
'constituency' => array(),
'ward' => array(),
'current_county' => false,
'current_constituency' => false
);
// print_r($return_array);
// collect the posted values from the submitted form
$make = key_exists('county', $_POST) ? $_POST['county'] : false;
$model = key_exists('constituency', $_POST) ? $_POST['constituency'] : false;
$year = key_exists('ward', $_POST) ? $_POST['ward'] : false;
// populate the $return_array with the necessary values
if ($make) {
$return_array['current_county'] = $make;
$return_array['constituency'] = array_keys($makes_models_years[$make]);
if ($model) {
$return_array['current_constituency'] = $model;
$return_array['ward'] = $makes_models_years[$make][$model];
if ($year) {
$return_array['current_ward'] = $year;
}
}
}
// encode the $return_array as a JSON object and echo it
echo json_encode($return_array);
print_r($return_array);
die();
?>

Answer 1

I realised that the issue was in the post not being able to read data returned by the php file. I solved it by placing the php file in the same directory as the javascript file, apparently they don't work well when in placed separate folders.