StorageArea.set()

let settingItem = browser.storage.<storageType>.set(
  keys             // object
)

function setItem() {
  console.log("OK");
}
function gotKitten(item) {
  console.log(`${item.kitten.name} has ${item.kitten.eyeCount} eyes`);
}
function gotMonster(item) {
  console.log(`${item.monster.name} has ${item.monster.eyeCount} eyes`);
}
function onError(error) {
  console.log(error);
}
// define 2 objects
let monster = {
  name: "Kraken",
  tentacles: true,
  eyeCount: 10,
};
let kitten = {
  name: "Moggy",
  tentacles: false,
  eyeCount: 2,
};
// store the objects
browser.storage.local.set({ kitten, monster }).then(setItem, onError);
browser.storage.local.get("kitten").then(gotKitten, onError);
browser.storage.local.get("monster").then(gotMonster, onError);