Indexed DB + Promises #3

@ Indexed DB Promises.md

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

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

I still think I'd like IDBRequest and IDBTransaction to have then and catch methods that proxy to an underlying promise. Seems like forgetting to add .promise is going to be common.

@domenic I guess this idea makes you sick in your mouth?

Thanks, @jakearchibald !

Promise properties should vend the same promise each time. So tx.promise === tx.promise.

Fixed in the "roughly equivalent to" example. Already present in the polyfill and normative text.

Guess this should be await tx.promise;

Yes, I missed a few of those. Bleah. Added 'em in.

I think I prefer .complete, but earlier you call it .promise.

I'd switched over but forgot when I made some edits. Corrected - it's .complete everywhere.

Unfortunately they can throw errors, which would violate http://www.w3.org/2001/tag/doc/promises-guide#always-return-promises if they returned promises

Bleah, good catch. Will ponder.

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;
}