Indexed DB + Promises #3

@ Indexed DB Promises.md

Moved to: https://github.com/inexorabletash/indexeddb-promises

... to support more fine-grained commenting and collaboration.

One option for IDBCursor's advance()/continue() would be to have them return an IDBRequest which then has .promise hanging off of it. The question is: what IDBRequest? Those methods currently reset the readyState of the original IDBRequest used to open the cursor from "done" back to "pending" and fire off new "success" or "error" events.

How about

• cursor() and advance() return the same IDBRequest originally used to open the cursor (NOTE: I've wanted this in other polyfills!)
• Generate a new internal, unfulfilled Promise (the one returned by .promise) for the request at the same time as the readyState is reset

So rq.promise === rq.promise would still hold, just not over time. Iteration would then look like:

async function getAll(store, query) {
  let result = [];
  let cursor = await store.openCursor(query).promise;
  while (cursor) {
    result.push(cursor.value);
    cursor = await cursor.continue().promise; // only change
  }
  return result;
}