| <head> | |
| <script> | |
| navigator.serviceWorker.addEventListener('message', event => { | |
| if (event.data != "echo") | |
| return; | |
| navigator.serviceWorker.getRegistration().then(function(registration) { | |
| registration.active.postMessage("echo back"); | |
| }); | |
| }); | |
| </script> | |
| </head> | |
| <body> | |
| </body> |