为什么window.location.href没有完成$ .post ...？

I am making a game for class and as with most games users are required to complete a level before moving on to the next. On my first level I use this under the If statement that determines if the user has won the level:

if (passOnLevel == 0 && passengerCarrying == 0) {
    alert("You Win!");
    $.post("gameL2.php", {"Level1": "Level1"});
    window.location.href='gameL2.php';
}

In my gameL2.php file I have this at the top of the file:

<?php session_start(); ?>
<?php
if (isset($_POST['Level1'])) {
$_SESSION['Level1'] = $_POST['Level1'];
}
 ?>

The issue I am having is that when I use window.location.href='gameL2.php; the $_POST is not set however if I removed window.location.href='gameL2.php; it doesn't redirect the user to the next level but when I access the gameL2.php file directly the $_POST is set. How can I make it redirect the users to level two but still set the post variable?

Problem is that $.post is asynchronous command, so when you call it, you are calling location.href right afterwards and $.post did not have time to actually do the post.

So what you need to do is this:

if (passOnLevel == 0 && passengerCarrying == 0) {
    alert("You Win!");
    $.post("gameL2.php", {"Level1": "Level1"}, function() {
      window.location.href='gameL2.php';
    });
}

Basically you are passing a function that $.post will call when it finishes. More at https://api.jquery.com/jQuery.post/

BUt, this will not resolve your problem with $_POST being unset in the second file, because calling $.post and opening gameL2.php are two calls, and data sending does not work that way.

So, in the end, you would probably be best off with:

if (passOnLevel == 0 && passengerCarrying == 0) {
    alert("You Win!");
    window.location.href='gameL2.php?Level1=Level1';
}

And then checking for $_GET["Level1"] in your gameL2.php