Access localStorage from service worker

Question

I want to periodically call an API from my service worker to send data stored in the localStorage. This data will be produced and saved in localStorage when a user browses my website. Consider it something like saving stats in localStorage and sending it periodically through the service worker. How should I do this? I understand that I can't access localStorage from service worker and will have to use the postMessage API. Any help would be highly appreciated.

Answer 1

You cannot access localStorage (and also sessionStorage) from a webworker process, they result will be undefined, this is for security reasons.

You need to use postMessage() back to the Worker's originating code, and have that code store the data in localStorage.

Use should use localStorage.setItem() and localStorage.getItem() to save and get data from local storage.

More infos:

Worker.postMessage()

Window.localStorage

Pseudo code below, hoping to get you start.

 // include your worker
 var myWorker = new Worker('YourWorker.js'),
   data,
   changeData = function() {
     // save data to local storage
     localStorage.setItem('data', (new Date).getTime().toString());
     // get data from local storage
     data = localStorage.getItem('data');
     sendToWorker();
   },
   sendToWorker = function() {
     // send data to your worker
     myWorker.postMessage({
       data: data
     });
   };
 setInterval(changeData, 1000)

Answer 2

https://developer.mozilla.org/en-US/docs/Web/API/Service_Worker_API/Using_Service_Workers says

Note: localStorage works in a similar way to service worker cache, but it is synchronous, so not allowed in service workers.

Note: IndexedDB can be used inside a service worker for data storage if you require it.

Also there is a bit of discussion here: How do I access the local storage using service workers in angular?