Passing variables withing the previewURL get lost on server side

[virgodesign]

I'm experiencing the following problem and I don't know exactly if it's a bug or a normal behavior.
I'm trying to pass a custom variable within the previewUrl using the wp.customize javascript object as following:

wp.customize.previewer.previewUrl( 'http://www.example.com/?custom_var=1' );

and then call the refresh method to launch the ajax request

wp.customize.previewer.refresh();

To customize the preview that will return back to the customizer we need to perform a check as following:

function load_custom_template( $template ) {
    
    	if( is_customize_preview() && isset($_GET['custom_var']) ) {
    		
    			$new_template = locate_template( array( 'custom_template.php' ) );
    			if ( '' != $new_template ) {
    				return $new_template ;
    			}
    		
    		}
    	}
    	
    	return $template;
    
    }
    add_filter( 'template_include', 'load_custom_template', 99 );

But when we try to retrieve the $_GET variable, this is missing.
The REQUEST_URI seems to have no get variables.

[westonruter]

@virgodesign calling wp.customize.previewer.refresh() should be unnecessary because merely changing the previewUrl should trigger a refresh with the newly-set URL.

[virgodesign]

@westonruter you are right. Without the refresh call the get variables are sended. But everthing should works fine even with the refresh method triggered manually. Anyway thanks for the suggestion. If this is not a defect/bug we can close the ticket.

[westonruter]

@virgodesign I can't reproduce the issue. I added this bit to my theme's header.php:

<?php echo esc_html( wp_json_encode( wp_unslash( $_GET ) ) ) ?>

And then I was able to enter this into the browser console:

var urlParser = document.createElement( 'a' );
urlParser.href = wp.customize.settings.url.home
urlParser.search = 'custom_var=1';
wp.customize.previewer.previewUrl( urlParser.href );

And the header showed the expected value:

{"custom_var":"1"}

Your issue may be that you tried to enter the wrong domain when setting the URL.

[virgodesign]

Could you try adding the refresh method, as following:

wp.customize.previewer.previewUrl( url );
wp.customize.previewer.refresh();

Without refresh there is no issue.
I can exclude that url entered is wrong.

[westonruter]

@virgodesign I tried with both, and there was no difference. Both worked as expected.

[virgodesign]

@westonruter, I'm not able to reproduce the error anymore. I'm supposing that could be a problem related to the expired session or an invalid nonce. Sometimes only after I refresh properly an admin page the system will prompt me with the message "Are you sure you want to do this?" or a login screen.