I can get the value of a storage key with the Chrome Extension API:
chrome.storage.sync.get(\"someKey\", function() {}
From the documentation (emphasis mine):
An empty list or object will return an empty result object. Pass in
null
to get the entire contents of storage. Don't forget to change "storage.sync" to storage.local if you're using local storage.
For some example code:
chrome.storage.sync.get(null, function(items) {
var allKeys = Object.keys(items);
console.log(allKeys);
});