How does WordPress’s `WP_Customize_Manager` handle settings that use `postMessage` transport?

Question

WordPress Expert — Medium

How does WordPress’s `WP_Customize_Manager` handle settings that use `postMessage` transport?

Accepted Answer

WordPress's `WP_Customize_Manager` uses postMessage transport to handle settings by having JavaScript on the preview frame listen for postMessage events from the customizer frame. This allows the theme to implement customize_preview_init JS that subscribes to setting changes via wp.customize() and applies them to the DOM without a page reload.