how to display alert in php

<?php 
// PHP program to pop an alert 
// message box on the screen 
  
// Display the alert box  
echo '<script>alert("Welcome to Geeks for Geeks")</script>'; 
  
?> 

echo '<script language="javascript">alert("juas");</script>';

javascript:alert('Email enviado com Sucesso!');
javascript:window.location='index.php';