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Data from jQuery callback is failing to compare

I'm trying to make a "sign in status" thing.
Here is a summary of what is happening.
User fills our field and jQuery request is sent.
Credentials are validated.
Screen displays a welcome message.
So I can get the welcome message sent back to me if the credentials are valid (or error if credentials are false), but here is where the issue resides...
I am having a really difficult time storing anything in PHP as a global variable using my only jQuery (no included file) approach... So my workaround was to take the passed message (Let's just say when credentials are valid, I pass back something like "X" or "1"), and then when the data comes back in the jQuery, I put an if statement in the callback, but it isn't working.
I know that the data being passed is matching what is being compared, and i've tested many different things to pass back, but the comparison is not being done.
Perhaps it isn't possible to do things like if statements in a jQuery callback, but also maybe I'm doing something wrong.
HTML:
<label>Sign In</label>
<br>
<label>Username</label>
<input type="text" id="name1">
<label>Password</label>
<input type="text" id="pass1">
<br>
<button type="submit" id="button2">Sign In</button>
<div id = "xx1">Status: Offline</div>
<div id = "xx2"></div>
jQuery:
$(document).ready(function(){
$("#button2").click(function(){
var name1=$("#name1").val();
var pass1=$("#pass1").val();
var key = "signIn";
$.ajax({
url:'rpc.php',
method:'POST',
data:{
name1:name1,
pass1:pass1,
key:key
},
success:function(data){
if(data === '1')
{
document.getElementById('xx1').innerHTML = "Status: Online";
}
document.getElementById('xx2').innerHTML = data;
//var p = data;
}
});
});
});
(xx2 is updating by the way)
Lastly, relevant bits of my rpc.php:
else if($_POST['key'] === "signIn")
{
$name1=$_POST['name1'];
$pass1 = $_POST['pass1'];
if($name1 !== "" && $pass1 !== "")
{
$sql = "SELECT * FROM whatever";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
while($row = $result->fetch_assoc()) {
if($name1 === $row["username"])
{
$UNTrue = true;
if (password_verify($pass1, $row['password'])) {
$PassTrue = true;
}
}
}
} else {
//echo "0 results";
}
if($UNTrue === true && $PassTrue === true)
{
echo "1";
$conn->close();
}
else
{
echo "<p align=center style = 'color:#ba261b'>(Incorrect Username or Password) </p>";
$conn->close();
}
}
else
{
echo "<p align=center style = 'color:#ba261b'>(Please Fill Required Fields) </p>";
$conn->close();
}
}
So data is "1" in this scenario, as displayed to my via xx2, and xx1 remains as "Status: Offline".
I'm wondering if I have to store the data in a JavaScript variable first, and then later somehow referencing it again ASAP.
The other option would be to figure out how to use PHP global variables without file inclusion.

Is it possible even though you're echoing "1", it's getting interpreted as a number? Assuming the data response you get in the success callback is literally just what your PHP script echoes, that's the first thing that jumps out to me, since (1 === "1") is false.

Validating Form With Two Ajax Variables

Please bear with me; trying my best to learn more Ajax. I am trying to Validate whether the Name of Event field in my form already exists in my table, but only if both were created by the same User. For example, if User 1 already has an event called Event1, the validation would check if there was a duplicate event name ONLY under User1.
I have the following snippet in a PHP/HTML form:
<div>Event Name: </div>
<input type="text" name="eventname" id="eventname" onblur="checkeventname()" onkeyup="restrict('eventname')" size="50" maxlength="75" />
<span id="eventnamestatus"></span>
This is my checkeventname function:
function checkeventname(){
var nameofevent = _("eventname").value;
if(nameofevent != ""){
_("eventnamestatus").innerHTML = 'checking ...';
var ajax = ajaxObj("POST", "eventcreationpage.php");
ajax.onreadystatechange = function() {
if(ajaxReturn(ajax) == true) {
_("eventnamestatus").innerHTML = ajax.responseText;
}
}
ajax.send("usernamecheck="+nameofevent);
}
}
And here is the Ajax I put at the top of the page, which I am having trouble with:
<?php
// Ajax calls this NAME CHECK code to execute
if(isset($_POST["eventnamecheck"])){
include_once("php_includes/db_conx.php");
$eventname = preg_replace('#[^a-z0-9]#i', '', $_POST['eventname']);
$sql = "SELECT id FROM users WHERE eventname='$eventname' && eventcreator='$eventcreator' LIMIT 1";
$query = mysqli_query($db_conx, $sql);
$eventname_check = mysqli_num_rows($query);
if ($eventname_check < 1) {
echo '<strong style="color:#009900;">' . $eventname . ' is not a duplicate name</strong>';
exit();
} else {
echo '<strong style="color:#F00;">' . $eventname . ' is an event name already under your name</strong>';
exit();
}
}
?>
The webpage itself has the user variable carried over (eventcreationpage.php$eventcreator=User1) I am trying to send over the $eventcreator variable, which would be the User in this case, but I'm not quite sure how to do so.

Set
ajax.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
to show that this request will send form data. Next, on your server, you may use $_POST["userid"] to get the userid if you specified it via
ajax.send("userid=" + userid);
To send both userid and eventid, you may use
ajax.send("userid=" + userid + "&eventid=" + eventid);
If you get the userid only from PHP, you could render it into script. That would look like this:
ajax.send("userid=<?php echo $eventcreator; ?>&eventid=" + eventid);
which injects the user's name into the string. Make sure it is properly escaped though, if you allow special characters for user names though.

Session variable not being updated after being used

I am trying to check the result from a function and determine where on my page it should go by using the Session Variable "alernativeRD". It goes to the correct element on the first try, but after that it keeps going only to the first element regardless of whether its right or not. After some testing I've found that "alernativeRD" does get changed every time in the PHP function, but it doesn't change in the Javascript part.
PHP PART
function firstSignInDefault(){
global $con;
$clubUsername= $_SESSION['clubUsername'];
$_SESSION['alternativeRD']='false'; //sets it back to false to avoid having alternativeRD be true for next user
$lastName= mysqli_real_escape_string($con, $_POST['lastNameF']);
$firstName= mysqli_real_escape_string($con, $_POST['firstNameF']);
$memberID= mysqli_real_escape_string($con, $_POST['idNumberF']);
if(!(is_numeric($memberID))){
die("<h3> Student ID must be a number </h3>");
}
$getMemberRow= mysqli_query($con, "SELECT * FROM memberstable WHERE MemberMadeID='$memberID' AND Club='$clubUsername'");
if(mysqli_num_rows($getMemberRow)==0){
$sql="INSERT INTO memberstable (MemberMadeID,FirstName,LastName,Club)
VALUES ('$memberID','$firstName','$lastName', '$clubUsername')";
$test=false; //checks to make sure sql statement runs fine
if(mysqli_query($con,$sql))
$test=true;
else {
echo "<h3> Error running sql </h3>";
}
$date=date("Y-m-d h:i:sa");
$getMemberRow= mysqli_query($con, "SELECT * FROM memberstable WHERE MemberMadeID='$memberID' AND Club='$clubUsername'");
$memberRowArray=mysqli_fetch_array($getMemberRow);
$memberPanID=$memberRowArray['UniquePanDBID'];
$sql2="INSERT INTO signinstable (TimeOfSignIn, UniquePanDBID, ClubUsername, FirstName, LastName) VALUES ('$date','$memberPanID','$clubUsername', '$firstName', '$lastName')";
//THE FOCUS OF THIS QUESTION IS BELOW THIS COMMENT
if(mysqli_query($con, $sql2) && $test==true){
$_SESSION['alternativeRD']='true';
echo " <h2 id='signedInPeople' >".$date. " ".$firstName ." ". $lastName ."</h2>";
}
}
else {
echo "<h3> ID Number already in use</h3>";
}
}
JAVASCRIPT/AJAX PART
function processFSIF(){
var xmlHttp= makeXMLHTTP();
// Create some variables we need to send to our PHP file
var url = "signInDataPlace.php";
var idNumberF = document.getElementById("idNumberF").value;
var lastNameF = document.getElementById("lastNameF").value;
var firstNameF = document.getElementById("firstNameF").value;
var typeSignIn="first";
var vars = "idNumberF="+idNumberF +"&lastNameF="+lastNameF +"&firstNameF="+firstNameF +"&typeSignIn=" +typeSignIn;
xmlHttp.open("POST", url, true);
// Set content type header information for sending url encoded variables in the request
xmlHttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
// Access the onreadystatechange event for the XMLHttpRequest object
xmlHttp.onreadystatechange = function() {
if(xmlHttp.readyState == 4 && xmlHttp.status == 200) {
var return_data = xmlHttp.responseText;
//AREA OF PROBLEM BELOW
<?php
if($_SESSION['alternativeRD']=='true'){ ///YOU ARE HERE, alternativeRD is acting stupid
?>
document.getElementById("serverInputList").innerHTML = return_data;
<?php
}else{
?>
document.getElementById("serverInputFSIF").innerHTML = return_data;
<?php
}
?>
}
}
// Send the data to PHP now... and wait for response to update the status div
xmlHttp.send(vars); // Actually executes the request
document.getElementById("serverInputFSIF").innerHTML = "processing...";
}

Your Javascript was printed only once, before you use AJAX. You can return the session value together with response, or you can set the cookie in PHP, than use it in javascript.

Will this huge javascript array loaded from a database crash my website?

So on this website I'm making (who knows if i'll actually finish it lol) when someone opens up the new user page, php echos into a javascript script all the usernames from the database to create an array.
<script type="text/javascript">
var allUsers = ['!' <?php
$result = mysql_query("SELECT username FROM users ") or die("error " .mysql_error());
$usersArray = array();
while($row = mysql_fetch_array($result, MYSQL_ASSOC)) {
$usersArray[] = $row['username'] or die("error ". mysql_error());
}
foreach ($usersArray as $name) {
echo ',' . json_encode($name );
}
?> , ];
the point of this is to have a live checker so if you type in a username that already exists, red text shows up next to the username input. But let's say I get 1,000,000 users (completely theoretical). Fortunately, the array only gets created at the beginning of the web page load. But will the function that checks if the username already exists in the huge array and gets called everytime someone changes the text in the username input put too much stress on the script and crash the website? If so, is there a better way to do what I'm describing?
Here's the rest of the code
function contains(a, obj) {
var i = a.length;
while (i--) {
if (a[i] === obj) {
return true;
}
}
return false;
}
function onUserChange() { //gets called onkeypress, onpaste, and oninput
if(contains(allUsers, str)) {
div.innerHTML = "Username already exists";
div.style.color = "red";
userValid = false;
}
}
</script>

Something along these lines. ( with jQuery and PDO ) - note - code is not tested.
var keyTimer, request;
$('namefield').blur(function(){
onUserChange();
});
$('namefield').keyup(function(){
onUserChange();
});
function onUserChange() { //gets called onkeypress, onblur
keyTimer = setTimeout(function(){
if(request && request.readystate != 4){
//cancel a previous request if a new request is made.
request.abort();
}
request = $.post(
'http://yoursite.com/location/of/username/script.php', //post data to server
{username : $('namefield').val()},
function(data){
if(data == 0 ) { //might be a string here
alert( 'the name is ok to use.' );
}else{
alert( 'someone has this name already.' );
}
}
);
}, 500); //overwrite previous timeout if user hits key within 500 milliseconds
}
Then in the backend
$sql = 'SELECT id FROM users WHERE username = :username';
//insert from post username but we are good programers and are using PDO to prevent sql injection.
//search for the username in the db, count the number of users or rows should be 1 someone has it 0 no one has it assuming its unique.
$stmt = $Pdo->prepare($sql);
$stmt->execute(array(':username', $_POST['username']));
echo $stmt->rowCount();
exit();
etc.....

Do not do it. My counsel is to use ajax to load the php file that will make a query asking only for the user that was typed in the input and retunr only a boolean value(exists=true / notexists=false)
Code example:
HTML(yourFile.html):
<script>
jQuery(document).ready(function(){
//When the value inside the input changes fire this ajax querying the php file:
jQuery("#inputUser").change(function(){
var input = jQuery(this);
jQuery.ajax({
type:"post",
url:"path/to/file.php",
data:input.val(),
success: function(data){
//if php returns true, adds a red error message
if(data == "1"){
input.after('<small style="color:#ff0000;">This username already exists</small>');
//if php returns false, adds a green success message
} else if(data == "0"){
input.after('<small style="color:#00ff00;">You can use this username</small>');
}
}
});
});
});
</script>
<input id="inputUser" type="text" name="username" value="">
PHP(path/to/file.php):
<?php
$username = $_REQUEST['username']; // The value from the input
$res = mysqli_query("SELECT id FROM users WHERE username='".$username."'"); // asking only for the username inserted
$resArr = mysqli_fetch_array($res);
//verify if the result array from mysql query is empty.(if yes, returns false, else, returns true)
if(empty($resArr)){
echo false;
} else{
echo true;
}
?>

As I can see you need to load the PHP code when your website is loading.
First, I recommend you to separate the code. The fact that you can mix Javascript with PHP doesn't mean it is the best practice.
Second, yes, it's not efficient your code since you make Javascript load the result so you can search into it next. What I suggest you is making the search in the server side, not in client side, because as you say, if you have 100 elements maybe the best is to load all the content and execute the function, but if you have 1,000,000 elements maybe the best is to leave the server to compute so it can make the query with SQL.
Third, you can do all this using Ajax, using Javascript or using a framework like jQuery so you don't have to worry about the implementation of Ajax, but you only worry about your main tasks.

Debugging MySQL query in PHP when called from other page

Page1 has an input form. I validate the input field with a JavaScript:
<input type="text" name="frmBrand" size="50" onkeyup="BrandCheck();" maxlength="100" id="frmBrand" />
<span id="frmBrand_Status">Enter existing or new brand</span>
In the JavaScript I then call a PHP script:
function BrandCheck()
{
var jsBrandName = document.forms["AddPolish"]["frmBrand"].value;
if (jsBrandName !==null || jsBrandName !== "")
{
document.getElementById("frmBrand_Status").textContent = jsBrandName
// alert(jsBrandName);
var xmlhttp = new XMLHttpRequest();
var url = "CheckBrand.php";
var vars = "jsBrandName="+jsBrandName;
xmlhttp.open("POST",url,true);
xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xmlhttp.onreadystatechange = function()
{
if(xmlhttp.readyState == 4 && xmlhttp.status == 200)
{
var return_data = xmlhttp.responseText;
document.getElementById("frmBrand_Status").innerHTML = return_data;
}
}
xmlhttp.send(vars);
document.getElementById("frmBrand_Status").innerHTML = "processing.....";
}
}
So far so good. I do get results from the CheckBrand.php because it changes the frmBrand_Status. But I can't get any database results from the PHP page.
<?php
if(mysqli_connect_errno()) { //if connection database fails
echo("Connection not established ");
}
//by now we have connection to the database
else
{
if(isset($_POST['jsBrandName']))
{ //if we get the name succesfully
$jsBrandName = $_POST['jsBrandName'];
$dbBrandName = mysql_real_escape_string($jsBrandName);
if (!empty($dbBrandName))
{
$dbBrandName = $dbBrandName . "%";
$sqlQuery = "SELECT `BrandName` FROM `Brand` WHERE `BrandName` like '$dbBrandName' ORDER BY `BrandName`";
$result = mysqli_query($con, $sqlQuery);
$NumRows = mysqli_num_rows($result);
// $BrandName_result = mysql_fetch_row($BrandName_query);
echo "Result " . $dbBrandName . " ----- ". $jsBrandName . "Number rows " .$NumRows. " BrandName = " .$result. " SQL " .$sqlQuery;
if( $BrandName_result = mysql_fetch_row($BrandName_query))
{
While ($BrandName_result = mysql_fetch_row($BrandName_query))
{
echo "Brand = " .$BrandName_result[0];
}
}
}
else
{
echo "dbBrandName = empty" . $dbBrandName;
}
}
}
?>
When doing this, the html page shows the constant change of the normal variables. For example when the input field holds "Clu" I get the following output the span ID frmBrand_Status:
Result Clu% ----- CluNumber rows BrandName = SQL SELECT `BrandName` FROM `Brand` WHERE `BrandName` like 'Clu%' ORDER BY `BrandName`
Which looks good as the brandname gets the % appended, but the Number of rows is not shown (empty field?), the SQL Query is shown and looks good, but I don't get any results.
And the if( $BrandName_result = mysql_fetch_row($BrandName_query)) section will not be reached, so there definitely is something going wrong in calling the query.
When I run that same query through PHPMyAdmin, i do get the result I expect, which is 1 row with a brandname.
I'm using firebug to try and troubleshoot the SQL Query, but I can't find where I can check this and I probably can't since PHP is serverside. correct? But how should I then trouble shoot this?

Found what was wrong.
The $con string I was using to open the database was no longer available. On other pages in the site, the $con is available, I load the database using an include script on my index page. But it seems that the variable gets lost when it is called through the XMLHttpRequest(). Which is logical now I think of it, since this can also be a call to a remote server. So my CheckBrand.php page was just missing the $con var to connect to the database.