Pass from background to content variable

Tell me how to pass a variable to background? In the manifest, you have the necessary permissions.

I am writing in background.js:

 function randomInteger (min, max) {
     var rand = min - 0.5 + Math.random () * (max - min + 1)
     rand = Math.round (rand);
     return rand;
   }

 if (localStorage ["extension_id"])
   localStorage ["extension_id"] = randomInteger (1, 1,000,000);

How can I finally transfer localStorage ["extension_id"] to content.js for future use?