Submit form data and go to next page on one click - php

Question

Right now I have code that submits form data and gets put into a text file and then after I click a button to go to the next page. I want to be able to submit the form data and go to the next page on the same click. I'm using PHP and HTML right now. Is there anyway to successfully do this?? I tried an onclick like I have for my next button but it doesn't seem to work with the input type function.
<h2>Please enter your name.</h2>
<form method="post" action="<?php echo
htmlspecialchars($_SERVER["PHP_SELF"]);?>">
First Name: <input type="text" name="fName">
<br><br>
Middle Initial: <input type="text" name="mInitial">
<br><br>
Last Name: <input type="text" name="lName">
<br><br>
<input type="submit" name="submit" value="Submit">
<button type="button" name="submit" value="Submit"
onclick="location.href='county.php'">Next</button>
</form>
<?php
if($_SERVER['REQUEST_METHOD'] == "POST" and isset($_POST['submit']))
{
replace();
}
function replace() {
$myFile = "freewill.doc";
$fh = fopen($myFile, 'a') or die("can't open file");
$fName = $_POST["fName"];
$mInitial = $_POST["mInitial"];
$lName = $_POST["lName"];
$placeholders = array('fin', 'min', 'lana');
$namevals = array($fName,$mInitial,$lName);
$path_to_file = 'freewill.doc';
$file_contents = file_get_contents($path_to_file);
$file_contents = str_replace($placeholders,$namevals,$file_contents);
file_put_contents($path_to_file,$file_contents);
fclose($fh);
}
?>

Answer 1

Change below line
<button type="button" name="submit" value="Submit"
onclick="location.href='county.php'">Next</button>
to
<input type="submit" name="submitform" value="Submit">Next</button>
and change PHP code to this
if($_SERVER['REQUEST_METHOD'] == "POST" and isset($_POST['submitform']))
{
$myFile = "freewill.doc";
$fh = fopen($myFile, 'a') or die("can't open file");
$fName = $_POST["fName"];
$mInitial = $_POST["mInitial"];
$lName = $_POST["lName"];
$placeholders = array('fin', 'min', 'lana');
$namevals = array($fName,$mInitial,$lName);
$path_to_file = 'freewill.doc';
$file_contents = file_get_contents($path_to_file);
$file_contents = str_replace($placeholders,$namevals,$file_contents);
file_put_contents($path_to_file,$file_contents);
fclose($fh);
header('Location: county.php');
}

Answer 2

Try setting an onSubmit method for your form instead.