URL variables like that are stored in the $_GET
variable. You can check the existence and value of one like this:
add_action(
'wp_head',
function() {
if ( isset( $_GET['feedback'] ) && 'yes' === $_GET['feedback'] ) {
?>
<script>
alert( 'Hello, world!' );
</script>
<?php
}
}
);
The check for isset()
is necessary as checking $_GET['feedback']
alone will throw an error if it’s not present in the URL at all.