Create StateStore class and specs for storing state in IndexedDB

spec/state-store-spec.js

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+/** @babel */
+import {it, ffit, fffit, beforeEach, afterEach} from './async-spec-helpers'
+
+const StateStore = require('../src/state-store.js')
+
+describe("StateStore", () => {
+  it("can save and load states", () => {
+    const store = new StateStore()
+    return store.save('key', {foo:'bar'})
+      .then(() => store.load('key'))
+      .then((state) => {
+        expect(state).toEqual({foo:'bar'})
+      })
+  })
+
+  describe("when there is an error reading from the database", () => {
+    it("rejects the promise returned by load", () => {
+      const store = new StateStore()
+
+      const fakeErrorEvent = {target: {errorCode: "Something bad happened"}}
+
+      spyOn(IDBObjectStore.prototype, 'get').andCallFake((key) => {
+        let request = {}
+        process.nextTick(() => request.onerror(fakeErrorEvent))
+        return request
+      })
+
+      return store.load('nonexistentKey')
+        .then(() => {
+          throw new Error("Promise should have been rejected")
+        })
+        .catch((event) => {
+          expect(event).toBe(fakeErrorEvent)
+        })
+    })
+  })
+})

src/state-store.js

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+'use strict'
+
+module.exports =
+class StateStore {
+  constructor () {
+    this.dbPromise = new Promise((resolve, reject) => {
+      let dbOpenRequest = indexedDB.open('AtomEnvironments', 1)
+      dbOpenRequest.onupgradeneeded = (event) => {
+        let db = event.target.result
+        db.createObjectStore('states')
+        resolve(db)
+      }
+      dbOpenRequest.onsuccess = () => {
+        resolve(dbOpenRequest.result)
+      }
+      dbOpenRequest.onerror = reject
+    })
+  }
+
+  save (key, value) {
+    return this.dbPromise.then(db => {
+      return new Promise((resolve, reject) => {
+        var request = db.transaction(['states'], 'readwrite')
+          .objectStore('states')
+          .put(value, key)
+
+        request.onsuccess = resolve
+        request.onerror = reject
+      })
+    })
+  }
+
+  load (key) {
+    return this.dbPromise.then(db => {
+      return new Promise((resolve, reject) => {
+        var request = db.transaction(['states'])
+          .objectStore('states')
+          .get(key)
+
+        request.onsuccess = (event) => resolve(event.target.result)
+        request.onerror = (event) => reject(event)
+      })
+    })
+  }
+}