Step 4 define the response actions when the servers

Step 4. Define the response actions when the server’s
response is received:
code for modern browsers

Define the response actions when the server’s
response is received:
code for modern browsers

Define the request that is sent “behind the scenes”
The request will send the userName value to valida%on.php,
which can access it using $ _GET [ 'userName '].
code for modern browsers

Send the request
AJAX for partial update of the page
DONE!!
<script>
function validation (){
var xmlhttp ;
if (window. XMLHttpRequest ){ // code for modern browsers
xmlhttp = new XMLHttpRequest ();
}else{ // code for old IE browsers
xmlhttp = new ActiveXObject (" Microsoft.XMLHTTP ");
}
xmlhttp . onreadystatechange = function (){
if ( xmlhttp . readyState == 4 && xmlhttp . status == 200 ){
document. getElementById (" responseMessage "). innerHTML = xmlhttp . responseText ;
}
}
a = document. getElementById (" userName ");
xmlhttp . open (" GET "," validation.php?userName= "+ a . value , true);
}
</script>
The Javascript code in example.html

PHP code on the server
Output
generated by
valida1on.php
Now, create validation.php for responding to the AJAX request.