example1.js

// Query current usage and availability in Temporary storage:
navigator.temporaryStorage.getInfo(
  function (info) {
    // Continue to initialize local cache using the obtained
    // usage and quota (availability) information.
    initializeCache(info);
  }, function (error) { log("Got error: ", error);
});

example2.js

function onError(error) {
  // Handle an error.
  log("Got error: ", error);
}

function setUpOfflineMode(availableSpace) {
  // ...
}

// A function which is to be called when 'offline-mode' is enabled.

function onOfflineEnabled(amountOfSpaceNeeded) {
  // First check how much we can use in the Persistent storage.
  navigator.persistentStorage.getInfo(
    function (info) {
      var availableSpace = info.quota - info.usage;
      if (availableSpace >= amountOfSpaceNeeded) {
        // We're fine; just continue to set up offline mode.
        setUpOfflineMode(availableSpace);
        return;
      }
      var requestingQuota = amountOfSpaceNeeded + info.usage;
      navigator.persistentStorage.requestQuota(
        requestingQuota,
        function (grantedQuota) {
          setUpOfflineMode(grantedQuota - info.usage);
        },
      onError);
    },
  onError);
}