如何使javascript响应php事件？

Question

I am developing a website for practice, and I would like to know how to use JS to notify the user that the username he picked is already in use, all works fine, if my function(check_username) returns false, the user succesfully registers himself into the site, otherwise the register won't happen.

When the user can't register I would like to know how can I notify the user with a js script.

<?php 
    //database includes
    include_once('../config/init.php');
    include_once('../database/users.php');

    if(!check_username($_POST['username'])) {
        insertUser($_POST['name'], $_POST['username'], $_POST['email'], $_POST['pass']);
    }
    else header('Location: ../index.php');
?>

Answer 1

One way would be to change your redirect on failure to a javascript message

else
{
  echo "<script>alert('Username already exists');</script>";
}

That's a very trivial example to get you started since you mentioned you're learning JS. You can build a lot of improvements on that.

Answer 2

You can set the returns into a javascript variable and use it to display message if the user is not registered.

var x = <?php echo check_username($_POST['username']); ?>;
if(x) {
    alert("You are not registered");
}

Answer 3

You can use php ajax for a live notification to users.

 <script> $(document).ready(function() { $("#InputFieldID").keyup(function (e) { //removes spaces from username $(this).val($(this).val().replace(/\\s/g, '')); //Getting value of input field. var username = $(this).val(); //Check only if the username characters are above 4 if(username.length >= 4){ $("#IndicatorDivID").html('<p style="color:#ffbf25;">Checking..!</p>'); $.ajax({ type: 'POST', url: 'check_username.php', data: {"username": username}, dataType: 'json', success: function (data) { if(data.response=='true') alert("Already Exist"); } }); } }); }); //Username Checker </script> 

The result fo check_username.php must be in json format. eg: {"response":"false"}