echo out php variable in jQuery - php

Question

this is changepassword.php file
<?php
include 'core/init.php';
if (empty($_POST) === false) {
if (md5($_POST['current_password']) === $user_data['password']) {
} else {
$errors[] = 'Your current psasword is incorrect';
}
}
if (empty($_POST) === false && empty($errors) === true) {
change_password($session_user_id, $_POST['password']);
} else if (empty($errors) === false) {
$error = output_errors($errors);
this variable
}
?>
this is the jQuery file
$('#save_pass').click(function(){
var current_password = $('#current').val();
var password = $('#new').val();
var password_again = $('#confirm').val();
if ((password == password_again) && (password.length >= 8)) {
$.post('changepassword.php', {current_password: current_password, password: password, password_again: password_again });
$('#show').html('password changed').fadeIn(500).delay(2000).fadeOut(500);
} else if ((current_password ==0) || (password_again.length == 0) || (password.length == 8)) {
$('#show').html('all fields are required').fadeIn(500).delay(2000).fadeOut(500);
} else {
$('#show').html('your password must be at least 8 characters').fadeIn(500).delay(2000).fadeOut(500); }
$('#current').val(null);
$('#new').val(null);
$('#confirm').val(null);
});
i want to echo out $error variable when a user enters an incorrect password and click on the change password button with id="#save_pass"

Answer 1

You cannot echo php variables within a javascript file. Instead, put the javascript in your php file and echo it there - eg:
<script>
function something() {
alert('<?php echo $error; ?>');
}
</script>

Answer 2

In order to get back the errors from your $.post() ajax call, you need to echo $errors in your php script. Then add a success/done function to your $.post():
$.post('changepassword.php', {current_password: current_password ...})
.done(function (data) {
alert(data);
}
This should be the basics for getting back the raw echo data, but look at $.post documentation for more guidance on how to refine this.