为什么我的确认“警报”对我的代码不起作用？

Question

This is a page of a web app, and the job is simple:

I can see the " alert " that asks me whether I want to confirm or not. Based on the answer, I move to other pages.

If i sent my " if " cicle, the "alert" it's showed. This is the code

<?php
session_start();
include('../Model/gestoreAccessi.php');
include('connect.php');
?>
<script> 
let result = confirm("Sei sicuro di voler procedere?");
</script>
<script>
if(!result)
    result = <?php header('Location: http://www.teamjg.altervista.org/Matteo/navbar.php');?>
else
    <?php
    session_start();
    session_unset();
    session_destroy();
    header('Location: http://www.teamjg.altervista.org/Matteo/index.html');
    ?>
</script>

Answer 1

So, before I answer your question; just a note. PHP and Js will run on different machines (even though you're testing it on your localhost, still consider them as different machines)

All PHP code is run, and executed on the backend before anything is sent to your browser, after which js code is executed. PHP does not understand JS syntax, it will only look at <? and ?> tags and execute everything inside them.

<?php
session_start();
include('../Model/gestoreAccessi.php');
include('connect.php');
?>
<script> 
let result = confirm("Sei sicuro di voler procedere?");
</script>
<script>
if(!result)
    result = <?php header('Location: http://www.teamjg.altervista.org/Matteo/navbar.php');?>
else
    <?php
    session_start();
    session_unset();
    session_destroy();
    header('Location: http://www.teamjg.altervista.org/Matteo/index.html');
    ?>
</script>

When this code is being sent by XAMPP (or whatever engine you use), the PHP is first executed which will make the code look like this:

// Session will be started
// contents of ../Model/gestoreAccessi.php will be copied and run
// contents of connnect.php will be copied and run
<script> 
let result = confirm("Sei sicuro di voler procedere?");
</script>
<script>
if(!result)
    result = //The header is already set
else
    // Location is already set
</script>

So this is undefined behaviour as you are sending two header tags with different locations, my best guess is it will redirect to http://www.teamjg.altervista.org/Matteo/index.html .

One thing you could do as a hotfix is set window.location.href if you want to redirect your user to some other website. Read this .