How to get JS to read the code thrown by PHP die - php

Question

My JS function expects a certain return from the PHP code in case of a failure.
function showResult(data)
{
if (data == 'save_failed') {
document.getElementById('result').innerHTML = 'Unfortunately, we were not able to save your information. Please contact an admin.';
return false;
} else {
$("#notify").clearForm().clearFields().resetForm();
document.getElementById('result').innerHTML = 'Thank you for signing up with us.';
return false;
}
}
This works fin when I echo 'save_failed'; in case of an explicit error, but it does not work in the case of die statements, such as this one:
mysql_connect("host", "user", "pass") or die('save_failed');
I entered a wrong hostname but the JS function did not receive the 'save_failed' return.
PHP script:
if (!(empty($_POST['name']) && empty($_POST['email'])))
{
//sanitizing inputs for MySQL insertion
$name = mysql_real_escape_string($_POST['name']);
$email = mysql_real_escape_string($_POST['email']);
//connecting to db
mysql_connect("host", "user", "pass") or die('save_failed');
mysql_select_db("table") or die('save_failed');
//inserting into table
mysql_query("INSERT INTO notify (name, email) VALUES('" . $name . "', '" . $email . "' ) ")
or die('save_failed');
}
else
{
echo 'save_failed';
}

Answer 1

Even though die("save_failed") will output "save_failed", it will not stop any previous output in your script from being sent.
Ensure that if you go to the script yourself then you are receiving just "save_failed" in the page source and no erroneous characters

Answer 2

I would propose another strategy in dealing with errors.
Use output buffering to ensure no data will be send to client (eg. the beginning of a HTML-Document)
Start using Exceptions. They represent fatal errors, but with the ability to determine the exact line and parameters the error occurred.
The Browser tries to evaluate the type of response based on the content type header. If you want it to display simple text use
header('Content-Type: text/plain');
Use a global Exception handler, to transform the messages the way you like.
Works for me! Most servers have enough power today to use these, little more advanced methods.

Answer 3

It is not a good idea to use die to pass some information to the page. Normally, there will be other data in the response string.
An easier way is to embed PHP code in your JS code. An example will be like this:
<script type="text/javascript">
data = "<?php echo('Save Failed'); ?>";
</script>