$_POST value returns blank/empty - php

Question

I do have a form where the user can retrieve the data depending on the dates selected. Here's what I have:
<form class="form" method="post">
<div class="form-row">
<div class="form-group col-md-2 col-5">
<label class="col-form-label col-form-label-sm" for="From">From</label>
<input type="date" class="form-control" id="fromDate" name="fromDate" value="<?php echo (new DateTime('first day of this month'))->format('Y-m-d');?>">
</div>
<div class="form-group col-md-2 col-5">
<label class="col-form-label col-form-label-sm" for="To">To</label>
<input type="date" class="form-control" id="toDate" name="toDate" value="<?php echo (new DateTime('today'))->format('Y-m-d');?>">
</div>
<div class="form-group col-md-1 col-2">
<label class="col-form-label col-form-label-sm text-white" for="Search">Search</label>
<input type="button" class="btn btn-success btn-block" id="submit" name="submit" value="Submit" onclick="getResult()">
</div>
</div>
</form>
<div id="data_result"></div>
On the same page, I have a script below:
<script>
function getResult(){
var fm = $('#fromDate').val();
var to = $('#toDate').val();
$.ajax({
method: 'POST',
url: 'chart-data/card-sales.php',
data: { fm:fm, to:to },
success: function(data) {
$('#data_result').html(data);
}
});
}
</script>
And finally, my chart-data/card-sales.php file:
<?php
// db settings
$hostname = 'localhost';
$username = 'root';
$password = 'password';
$database = 'accounts';
// db connection
$con = mysqli_connect($hostname, $username, $password, $database) or die("Error " . mysqli_error($con));
$fm = '';
$to = '';
if(isset($_POST['fromDate'],$_POST['toDate']))
{
$date1 = strtr($_POST['fromDate'], '/', '-');
$fm = date('Y-m-d',strtotime($date1));
$date2 = strtr($_POST['toDate'], '/', '-');
$to = date('Y-m-d',strtotime($date2));
} else {
var_dump($_POST);
}
echo'<div id="data_result">
<h6>
<span class="text-danger">'.$fm.'</span> to
<span class="text-danger">'.$to.'</span>
</h6>';
$sql="SELECT * FROM sales WHERE date >='$fm' and date <= '$to'";
foreach ($con->query($sql) as $row) {
echo'//table contents';
};
echo '</div>';
?>
The thing is, $fm and $to returns an empty value (1970-01-01) that is why I couldn't get the proper data I need while the var_dump($_POST); returns array(2) { ["fm"]=> string(10) "2021-01-01" ["to"]=> string(10) "2021-01-26" }. So I think the main problem here is that I cannot get the input value from my form. Why is that so?

Answer 1

The problem is that you're not using the correct indexes on $_POST.
You should use the same indexes that you sent in the ajax: fm and to.
Change this:
if(isset($_POST['fromDate'],$_POST['toDate']))
{
$date1 = strtr($_POST['fromDate'], '/', '-');
$fm = date('Y-m-d',strtotime($date1));
$date2 = strtr($_POST['toDate'], '/', '-');
$to = date('Y-m-d',strtotime($date2));
} else {
var_dump($_POST);
}
To this:
if(isset($_POST['fm'], $_POST['to']))
{
$date1 = strtr($_POST['fm'], '/', '-');
$fm = date('Y-m-d',strtotime($date1));
$date2 = strtr($_POST['to'], '/', '-');
$to = date('Y-m-d',strtotime($date2));
} else {
var_dump($_POST);
}
P.S: Yo should take a look about SQL injection and prepared queries as #Strawberry suggested.
I encourage you to change to an object-oriented aproach using PDO

Answer 2

As you send in your ajax call, data: {fm: fm, to: to} this is what to use.
Try to change:
if (isset ($_POST['fromDate'], $_POST['toDate']))
{
$date1 = strtr($_POST['fromDate'], '/', '-');
...
$date2 = strtr($_POST['toDate'], '/', '-');
...
}
by
if (isset ($_POST['fm'], $_POST['to']))
{
$date1 = strtr($_POST['fm'], '/', '-');
...
$date2 = strtr($_POST['to'], '/', '-');
...
}