Redirect from php file to html - php

Question

Here my php code. I need to redirect to another page when if($users[$name] === $password) or when $users[$name] = $password; but it does not work.What is wrong?Here ajax too.
$(document).ready(function() {
$('#submit').click(function() {
var name = $('#username').val();
var password = $('#password').val();
$.ajax({
type: 'POST',
url: 'php/login_script.php',
data: {
user: name,
pass: password
},
success: function(a) {
alert(a);
}
});
});
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<?php
if(!isset($_POST['user'])||!isset($_POST['pass'])){
die();
}
$file = "users.json";
$users = json_decode(file_get_contents($file), true);
$name = $_POST['user'];
$password = $_POST['pass'];
if(isset($users[$name])) {
if($users[$name] === $password){
header("Location:chat.html");
exit;
}
else {
echo "Wrong password";
}
}
else {
$users[$name] = $password;
file_put_contents($file, json_encode($users, JSON_PRETTY_PRINT));
header("Location:chat.html");
exit;
}

Answer 1

Because you're fetching the page with ajax the redirection will happen to the ajax request which means you will get back a 301 response.
This should work:
$(document).ready(function() {
$('#submit').click(function() {
var name = $('#username').val();
var password = $('#password').val();
$.ajax({
type: 'POST',
url: 'php/login_script.php',
data: {
user: name,
pass: password
},
success: function(a) {
document.location = 'chat.html';
},
error: function() {
alert('Invalid password');
}
});
});
});
and
<?php
if(!isset($_POST['user'], $_POST['pass']) || empty($_POST['user']) || empty($_POST['pass'])){
// Send bad request so redirect doesn't happen
http_response_code(400);
die();
}
$file = "users.json";
$users = json_decode(file_get_contents($file), true);
$name = $_POST['user'];
$password = $_POST['pass'];
if(isset($users[$name])) {
if($users[$name] != $password){
http_response_code(400);
echo "Wrong password";
}
}
else {
$users[$name] = $password;
file_put_contents($file, json_encode($users, JSON_PRETTY_PRINT));
}
This will return 200 on success and 400 on failure which will trigger the success and error parts of the $.ajax request.

Answer 2

The thing you need to realize about PHP is all of the PHP stuff is done before sending the page to the user, so calling a redirect on php/login_script.php does nothing.
What you need to do is return something to indicate success of the login.
Here's what you should do to understand my explanation:
Replace header("Location:chat.html"); with echo "success"; in your PHP code.
Change your jQuery to the following:
success: function(a)
{
if (a === "success")
{
window.location.replace("chat.html");
}
}