musix-oss/node_modules/idb/README.md

IndexedDB Promised

This is a tiny library that mirrors IndexedDB, but replaces the weird IDBRequest objects with promises, plus a couple of other small changes.

Installation

If you're using Rollup/Webpack or similar:

npm install idb

Then in your JS:

import { openDb, deleteDb } from 'idb';

await openDb(…);

Or include the script as it is, and idb will exist on the global scope.

Changes from 2.x

The library is now a module. To take advantage of this, importing has changed slightly:

// Old 2.x way:
import idb from 'idb';
idb.open(…);
idb.delete(…);

// New way:
import { openDb, deleteDb } from 'idb';
openDb(…);
deleteDb(…);

Examples

Keyval Store

This is very similar to localStorage, but async. If this is all you need, you may be interested in idb-keyval, you can always upgrade to this library later.

const dbPromise = openDb('keyval-store', 1, upgradeDB => {
  upgradeDB.createObjectStore('keyval');
});

const idbKeyval = {
  async get(key) {
    const db = await dbPromise;
    return db.transaction('keyval').objectStore('keyval').get(key);
  },
  async set(key, val) {
    const db = await dbPromise;
    const tx = db.transaction('keyval', 'readwrite');
    tx.objectStore('keyval').put(val, key);
    return tx.complete;
  },
  async delete(key) {
    const db = await dbPromise;
    const tx = db.transaction('keyval', 'readwrite');
    tx.objectStore('keyval').delete(key);
    return tx.complete;
  },
  async clear() {
    const db = await dbPromise;
    const tx = db.transaction('keyval', 'readwrite');
    tx.objectStore('keyval').clear();
    return tx.complete;
  },
  async keys() {
    const db = await dbPromise;
    return db.transaction('keyval').objectStore('keyval').getAllKeys(key);
  },
};

Usage

idbKeyval.set('foo', {hello: 'world'});

// logs: {hello: 'world'}
idbKeyval.get('foo').then(val => console.log(val));

Set of objects

Imagine we had a set of objects like…

{
  "id": 123456,
  "data": {"foo": "bar"}
}

Upgrading existing DB

const dbPromise = openDb('keyval-store', 2, upgradeDB => {
  // Note: we don't use 'break' in this switch statement,
  // the fall-through behaviour is what we want.
  switch (upgradeDB.oldVersion) {
    case 0:
      upgradeDB.createObjectStore('keyval');
    case 1:
      upgradeDB.createObjectStore('objs', {keyPath: 'id'});
  }
});

Adding

dbPromise.then(db => {
  const tx = db.transaction('objs', 'readwrite');
  tx.objectStore('objs').put({
    id: 123456,
    data: {foo: "bar"}
  });
  return tx.complete;
});

Getting all

dbPromise.then(db => {
  return db.transaction('objs')
    .objectStore('objs').getAll();
}).then(allObjs => console.log(allObjs));

Getting by ID

dbPromise.then(db => {
  return db.transaction('objs')
    .objectStore('objs').get(123456);
}).then(obj => console.log(obj));

Limitations

Transaction lifetime

An IDB transaction will auto-close if it doesn't have anything to do once microtasks have been processed. As a result, this works fine:

dbPromise.then(async db => {
  const tx = db.transaction('keyval', 'readwrite');
  const store = tx.objectStore('keyval');
  const val = await store.get('counter') || 0;
  store.put(val + 1, 'counter');
  return tx.complete;
});

But this doesn't:

dbPromise.then(async db => {
  const tx = db.transaction('keyval', 'readwrite');
  const store = tx.objectStore('keyval');
  const val = await store.get('counter') || 0;
  // The transaction will auto-close while the fetch is in-progress
  const newVal = await fetch('/increment?val=' + val)
  store.put(newVal, 'counter');
  return tx.complete;
});

Promise issues in older browsers

Some older browsers don't handle promises properly, which causes issues if you do more than one thing in a transaction:

dbPromise.then(async db => {
  const tx = db.transaction('keyval', 'readwrite');
  const store = tx.objectStore('keyval');
  const val = await store.get('counter') || 0;
  // In some older browsers, the transaction closes here.
  // Meaning this next line fails:
  store.put(val + 1, 'counter');
  return tx.complete;
});

All modern browsers have fixed this. Test your browser.

You can work around this in some versions of Firefox by using a promise polyfill that correctly uses microtasks, such as es6-promise.

API

idb

This is your entry point to the API. It's exposed to the global scope unless you're using a module system such as browserify, in which case it's the exported object. If you are using native ES modules, the functions are provided as individual exports, so you can import * as idb from 'idb' or import { openDb, deleteDb } from 'idb'.

openDb(name, version, upgradeCallback)

This method returns a promise that resolves to a DB.

name and version behave as they do in indexedDB.open.

upgradeCallback is called if version is greater than the version last opened. It's similar to IDB's onupgradeneeded. The callback receives an instance of UpgradeDB.

openDb('keyval-store', 2, upgradeDB => {
  // Note: we don't use 'break' in this switch statement,
  // the fall-through behaviour is what we want.
  switch (upgradeDB.oldVersion) {
    case 0:
      upgradeDB.createObjectStore('keyval');
    case 1:
      upgradeDB.createObjectStore('stuff', {keyPath: ''});
  }
}).then(db => console.log("DB opened!", db));

deleteDb(name)

Behaves like indexedDB.deleteDatabase, but returns a promise.

deleteDb('keyval-store').then(() => console.log('done!'));

DB

Properties:

• Same as equivalent properties on an instance of IDBDatabase:
  • name
  • version
  • objectStoreNames

Methods:

• close - as idbDatabase.close
• transaction - as idbDatabase.transaction, but returns a Transaction

UpgradeDB

As DB, except:

Properties:

• transaction - this is a property rather than a method. It's a Transaction representing the upgrade transaction
• oldVersion - the previous version of the DB seen by the browser, or 0 if it's new

Methods:

• createObjectStore - as idbDatabase.createObjectStore, but returns an ObjectStore
• deleteObjectStore - as idbDatabase.deleteObjectStore

Transaction

Properties:

• complete - a promise. Resolves when transaction completes, rejects if transaction aborts or errors
• Same as equivalent properties on an instance of IDBTransaction:
  • objectStoreNames
  • mode

Methods:

• abort - as idbTransaction.abort
• objectStore - as idbTransaction.objectStore, but returns an ObjectStore

openDb('keyval-store', 1, upgradeDB => {
  switch (upgradeDB.oldVersion) {
    case 0:
      upgradeDB.createObjectStore('keyval');
  }
}).then(db => {
  const tx = db.transaction('keyval', 'readwrite');
  tx.objectStore('keyval').put('hello', 'world');
  return tx.complete;
}).then(() => console.log("Done!"));

ObjectStore

Properties:

• Same as equivalent properties on an instance of IDBObjectStore:
  • name
  • keyPath
  • indexNames
  • autoIncrement

Methods:

• Same as equivalent methods on an instance of IDBObjectStore, but returns a promise that resolves/rejects based on operation success/failure:
  • put
  • add
  • delete
  • clear
  • get
  • getAll
  • getAllKeys
  • count
• Same as equivalent methods on an instance of IDBObjectStore, but returns a promise that resolves with a Cursor:
  • openCursor
  • openKeyCursor
• deleteIndex - as idbObjectStore.deleteIndex
• Same as equivalent methods on an instance of IDBObjectStore, but returns an Index:
  • createIndex
  • index
• iterateCursor - see below
• iterateKeyCursor - see below

iterateCursor & iterateKeyCursor

Due to the microtask issues in some browsers, iterating over a cursor using promises doesn't always work:

const tx = db.transaction('stuff');
tx.objectStore('stuff').openCursor().then(function cursorIterate(cursor) {
  if (!cursor) return;
  console.log(cursor.value);
  return cursor.continue().then(cursorIterate);
});
tx.complete.then(() => console.log('done'));

So in the mean time, iterateCursor and iterateKeyCursor map to openCursor & openKeyCursor, take identical arguments, plus an additional callback that receives an IDBCursor, so the above example becomes:

const tx = db.transaction('stuff');
tx.objectStore('stuff').iterateCursor(cursor => {
  if (!cursor) return;
  console.log(cursor.value);
  cursor.continue();
});
tx.complete.then(() => console.log('done'));

The intent is to remove iterateCursor and iterateKeyCursor from the library once browsers support promises and microtasks correctly.

Index

Properties:

• Same as equivalent properties on an instance of IDBIndex:
  • name
  • keyPath
  • multiEntry
  • unique

Methods:

• Same as equivalent methods on an instance of IDBIndex, but returns a promise that resolves/rejects based on operation success/failure:
  • get
  • getKey
  • getAll
  • getAllKeys
  • count
• Same as equivalent methods on an instance of IDBIndex, but returns a promise that resolves with a Cursor:
  • openCursor
  • openKeyCursor
• iterateCursor - as objectStore.iterateCursor but over the index
• iterateKeyCursor - as objectStore.iterateKeyCursor but over the index

Cursor

Properties:

• Same as equivalent properties on an instance of IDBCursor:
  • direction
  • key
  • primaryKey
  • value

Methods:

• Same as equivalent methods on an instance of IDBCursor, but returns a promise that resolves/rejects based on operation success/failure:
  • update
  • delete
• Same as equivalent methods on an instance of IDBCursor, but returns a promise that resolves with a Cursor:
  • advance
  • continue
  • continuePrimaryKey