PHP和Javascript电子邮件验证'@'符号

Question

Trying to get code to search if '@' symbol is present in typed-in email address and echo if symbol is not. Everything works fine without the searching for @ code.

check.php

<?php
include '/connect.php'; //connects to mysql

$email = mysqli_real_escape_string($connect, $_POST['email']);

$check = mysqli_query($connect, "SELECT email FROM users WHERE email='$email'");
$check_num_rows = mysqli_num_rows($check);

if ($email==NULL) {
    echo 'Enter an email';
} elseif (strlen($email)<6) {
    echo 'Please enter a valid email';
} elseif (str($email).indexOf('@') == -1) {
    echo 'Please enter a valid email';
} else {
    if ($check_num_rows==0) {
        echo 'Email valid';
    } elseif ($check_num_rows==1) {
        echo 'Email already registered';
    }
}

register.php

<script type="text/javascript" src="/jquery-3.2.1.min.js"></script>

<script>
    $(document).ready(function() {
       $('#feedback_email').load('/check.php').show();

       $('#email').keyup(function() {
           $.post('/check.php', { email: form.email.value }, 
           function(result) {
               $('#feedback_email').html(result).show;
           });
       });
    });
</script>

<form action="register.php" method="post" name="form">

<input id="email" type="text" name="email" placeholder="Email Address" maxlength="60" value="<?php if (isset($trimmed['email'])) echo $trimmed['email']; ?>">

<div id="feedback_email"></div>

<p><center><input type="submit" name="submit" value="Register"></center>
</form>

EDIT: I do have a built in filter for the php back-end validation. However, I'm trying to do a front-end validation as well through these codes. If anyone knows how to fix my script please post. I'm receiving error

Call to undefined function str() in /check.php on line 13

Line 13

} elseif (str($email).indexOf('@') == -1) {

Answer 1

A much better approach to validating the emails, would be to use the built in filters intended for that sort of thing

<?php

    include '/connect.php'; //connects to mysql

    $email = mysqli_real_escape_string($connect, $_POST['email']);

    $check = mysqli_query($connect, "SELECT email FROM users WHERE email='$email'");
    $check_num_rows = mysqli_num_rows($check);

    if ( filter_var($email, FILTER_VALIDATE_EMAIL) ) {
        if ($check_num_rows==0) {
            echo 'Email valid';
        } elseif ($check_num_rows==1) {
            echo 'Email already registered';
        }
    } else {
        echo 'Please enter a valid email';
    }
?>

The reason your code doesn't work, is because PHP doesn't have a str or indexOf method, you should be using something like strpos instead

if (strpos($email, '@') === false) { ...