Use wp_get_script_tag() and wp_get_inline_script_tag() in wp-includes/functions.php.

Author: enricocarraro

src/wp-includes/functions.php

@@ -6839,21 +6839,19 @@ function wp_post_preview_js() {
 	// Has to match the window name used in post_submit_meta_box().
 	$name = 'wp-preview-' . (int) $post->ID;
 
-	?>
-	<script>
-	( function() {
+	$js = '( function() {
 		var query = document.location.search;
 
-		if ( query && query.indexOf( 'preview=true' ) !== -1 ) {
-			window.name = '<?php echo $name; ?>';
+		if ( query && query.indexOf( "preview=true" ) !== -1 ) {
+			window.name = "' . $name . '";
 		}
 
 		if ( window.addEventListener ) {
-			window.addEventListener( 'unload', function() { window.name = ''; }, false );
+			window.addEventListener( "unload", function() { window.name = ""; }, false );
 		}
-	}());
-	</script>
-	<?php
+	}());';
+
+	wp_print_inline_script_tag( $js );
 }
 
 /**