async-local-storage

This is a p(r)ollyfill for a fully-async object-storage API that's simpler than IndexedDB, but also async, removing many of the performance hazards of localStorage.

The API is roughly mirrors the ES6 Map type, but all methods return Future instances to enable async operation.

To get started quickly, use one of the pre-built versions from the bin/ directory. To work from source, make sure you git submodule update --init after cloning.

API

The API lives at navigator.storage to distinguish it from window.localStorage and to prevent introducing a new global symbol,

Methods:

var storage = navigator.storage ||          // New API, new object
              navigator.alsPolyfillStorage; // Where the polyfill lives

storage.has(/*string*/ key)
    .then(function(bool) {});

storage.get(/*string*/ key)
    .then(function(value) {});

storage.set(/*string*/ key, /*cloneable*/ value)
    .then(function() {});

storage.delete(/*string*/ key)
    .then(function() {});

storage.clear()
    .then(function() {});

storage.count()
    .then(function(integer) {});

storage.forEach(/*function*/ callback, /*any*/ scope)
    .then(function() {});

Examples

var storage = navigator.storage ||
              navigator.alsPolyfillStorage;

// Testing for a value
storage.has("thinger").then(function(doesHaveThinger) {
  if (doesHaveThinger) {
    // ...
  }
});

// Getting a value
storage.get("thinger").then(
  function(value) {
    // ...
  },
  function(e) { console.log("get failed with error:", e); }
);

// Setting a value without error handling is simple:
storage.set("thinger", "blarg");

// But setting is also async, so to read related values, it's best to wait
storage.set("thinger", "othervalue").then(function() {
  storage.get("...").then(function(value) {
    // ...
  });
});

// Iteration is also async. The returned Future resolves when the passed
// callback has been invoked for each item (or when one fails, in case of error)
var itemCount = 0;
storage.forEach(function(value, key) {
  itemCount++;
}).then(function() { console.log(itemCount, "items in storage"); });

// The above is equivalent to using .count():
storage.count().then(function(c) { console.log(c, "items in storage"); });

Browser Support

This code is only meant to work on browsers with modern IndexedDB support and has been tested in stable-channel Chrome and Firefox as of Spring '13.

License

Apache v2 License. See the LICENSE file.