Checking for existing users in DB using Ajax and PHP - php

Question

I'm running into a problem where the code keeps on showing that the user name is available, even though it is existing in the DB. Can anyone solve the problem that I'm running into? Down below is my code.
PHP
// Define $username
$username=$_POST["emailAddress"];
// Create Connection
$db = new mysqli($server, $user, $password, $database);
// Check Connection
if ($db->connect_error) {
die("Connection failed: " . $db->connect_error);
}
// SQL query to fetch registerd users and finds user match.
$query = "SELECT email_address FROM users WHERE email_address='$username'";
$result = mysqli_query($db,$query);
$rows = mysqli_num_rows($result);
//if number of rows fields is bigger them 0 that means it's NOT available '
if($rows>0){
//and we send 0 to the ajax request
echo 0;
}else{
//else if it's not bigger then 0, then it's available '
//and we send 1 to the ajax request
echo 1;
}
mysqli_close($db); // Closing Connection
jQuery
$(document).ready(function () {
//when button is clicked
$('[name="checkAvail"]').on("click", function () {
check_availability();
});
});
//function to check username availability
function check_availability() {
//get the username
var username = $('[name="emailAddress"]').val();
//use ajax to run the check
$.post("checkusers.php",
function (result) {
//if the result is 1
if (result == 1) {
//show that the username is available
$('.existingUser').html(username + ' is Available');
} else {
//show that the username is NOT available
$('.existingUser').html(username + ' is NOT Available');
}
});
}
HTML
<div class="form-group">
<button class="btn btn-default" name="checkAvail">Check Availability</button>
<label for="emailAddress" class="col-sm-5 control-label">Email:</label>
<div class="col-sm-4">
<input type="email" class="form-control" id="emailAddress" name="emailAddress" placeholder="Email" autocomplete="off">
</div>
</div>

Answer 1

Your ajax doesn't send any data...so $_POST["emailAddress"]; is going to be empty in your php
You need to add a data object as second argument of $.post
$.post("checkusers.php",{emailAddress : username },function (result) {
// success handing code left out for clarity
});
Also you should check that the input isn't empty before user is allowed to check it. No point in sending invalid empty values to server.
There are lots of simple javascript validation plugins you can use.
Similarly on server should be valididating the user input. This is the most important point of validation because javascript can be worked around to allow sending anything

Answer 2

You aren't sending any data to the Post Page.
$.post( "checkusers.php", { emailAddress: username})
.done(function( data ) {
if (data == "1") {
//show that the username is available
$('.existingUser').html(username + ' is Available');
} else {
//show that the username is NOT available
$('.existingUser').html(username + ' is NOT Available');
}
});
Check the jQueryDocumentation

Answer 3

according to your php script try this if (result==0)
function (result) {
//if the result is 0
if (result == 0) {
//show that the username is available
$('.existingUser').html(username + ' is Available');
} else {
//show that the username is NOT available
$('.existingUser').html(username + ' is NOT Available');
}