Use AJAX Return value to PHP function - php

Question

My ajax successfully return the value but my problem is I can't use the value to my function. How do I convert this div to a value?
<?php
echo $ajax_user_id = '<div id="result"></div>'; //value can display here
getName($ajax_user_id); //value wont work here
?>
<form method="post" id="registerSubmit">
<input type="text" name="user_id" id="user_id">
<button id="submit" type="submit">Submit</button>
</form>
<script>
$(document).ready(function(){
$("#registerSubmit").submit(function( e ) {
e.preventDefault();
$.ajax({
url: "test.php",
method: "post",
data: $(this).serialize(),
dataType: "text",
success: function(Result) {
$('#result').text(Result)
}
})
});
});
</script>

Answer 1

You can't use it that way.because jQuery is a scripting language which runs in browser when DOM is fully loaded and elements are available to make selectors.While php is server side language which runs on server way before page load.anyway to fulfill your need you can try something like this.
<form method="post" id="registerSubmit">
<input type="text" name="user_id" id="user_id">
<button id="submit" type="submit">Submit</button>
</form>
<script>
$(document).ready(function(){
$("#registerSubmit").submit(function( e ) {
e.preventDefault();
$.ajax({
url: "test.php",
method: "post",
data: $(this).serialize(),
dataType: "text",
success: function(Result) {
$('#result').text(Result);
getNameAjax(Result);
}
})
});
});
function getNameAjax(val)
{
$.ajax({
type: "POST",
url: GetNameAjax.php,
data:{'user_id':val},
success: function(res){
$('#name').html(res);
}
});
}
</script>
GetNameAjax.php file you can write like this
$ajax_user_id=$_POST['user_id'];
function getName($ajax_user_id)
{
return "name on the basis of id";
}