Lazy-load IndexedDB

assets/javascripts/app/app.coffee

@@ -61,7 +61,7 @@
   bootOne: ->
     @doc = new app.models.Doc @DOC
     @docs.reset [@doc]
-    @doc.load @bootDB.bind(@), @onBootError.bind(@), readCache: true
+    @doc.load @start.bind(@), @onBootError.bind(@), readCache: true
     new app.views.Notice 'singleDoc', @doc
     delete @DOC
     return
@@ -72,21 +72,17 @@
       (if docs.indexOf(doc.slug) >= 0 then @docs else @disabledDocs).add(doc)
     @docs.sort()
     @disabledDocs.sort()
-    @docs.load @bootDB.bind(@), @onBootError.bind(@), readCache: true, writeCache: true
+    @docs.load @start.bind(@), @onBootError.bind(@), readCache: true, writeCache: true
     delete @DOCS
     return
 
-  bootDB: ->
+  start: ->
     for doc in @docs.all()
       @entries.add doc.toEntry()
       @entries.add type.toEntry() for type in doc.types.all()
       @entries.add doc.entries.all()
 
     @db = new app.DB()
-    @db.init(@start.bind(@))
-    return
-
-  start: ->
     @trigger 'ready'
     @router.start()
     @hideLoading()

assets/javascripts/app/db.coffee

@@ -4,14 +4,23 @@ class app.DB
   constructor: ->
     @useIndexedDB = @useIndexedDB()
 
-  init: (@_callback) ->
-    if @useIndexedDB
-      @initIndexedDB()
-    else
-      @callback()
+  db: (fn) ->
+    return fn @_db unless @useIndexedDB and @_db is undefined
+
+    if @callback isnt undefined
+      _callback = @callback
+      @callback = =>
+        _callback()
+        fn @_db
+        return
+      return
+
+    @callback = =>
+      @_db ?= false
+      delete @callback
+      fn @_db
       return
 
-  initIndexedDB: ->
     try
       req = indexedDB.open(NAME, @indexedDBVersion())
       req.onerror = @callback
@@ -21,20 +30,12 @@ class app.DB
       @callback()
     return
 
-  isEnabled: ->
-    !!@db
-
-  callback: =>
-    @_callback?()
-    @_callback = null
-    return
-
   onOpenSuccess: (event) =>
     try
-      @db = event.target.result
-      @db.transaction(['docs', app.docs.all()[0].slug], 'readwrite').abort() # https://bugs.webkit.org/show_bug.cgi?id=136937
+      @_db = event.target.result
+      @_db.transaction(['docs', app.docs.all()[0].slug], 'readwrite').abort() # https://bugs.webkit.org/show_bug.cgi?id=136937
     catch
-      @db = null
+      @_db = false
 
     @callback()
     return
@@ -53,7 +54,12 @@ class app.DB
     return
 
   store: (doc, data, onSuccess, onError) ->
-    txn = @db.transaction ['docs', doc.slug], 'readwrite'
+    @db (db) ->
+      unless db
+        onError()
+        return
+
+      txn = db.transaction ['docs', doc.slug], 'readwrite'
       txn.oncomplete = -> if txn.error then onError() else onSuccess()
 
       store = txn.objectStore(doc.slug)
@@ -63,9 +69,15 @@ class app.DB
       store = txn.objectStore('docs')
       store.put(doc.mtime, doc.slug)
       return
+    return
 
   unstore: (doc, onSuccess, onError) ->
-    txn = @db.transaction ['docs', doc.slug], 'readwrite'
+    @db (db) ->
+      unless db
+        onError()
+        return
+
+      txn = db.transaction ['docs', doc.slug], 'readwrite'
       txn.oncomplete = -> if txn.error then onError() else onSuccess()
 
       store = txn.objectStore(doc.slug)
@@ -74,22 +86,29 @@ class app.DB
       store = txn.objectStore('docs')
       store.delete(doc.slug)
       return
+    return
 
-  version: (doc, callback) ->
-    txn = @db.transaction ['docs'], 'readonly'
+  version: (doc, fn) ->
+    @db (db) ->
+      unless db
+        fn(false)
+        return
+
+      txn = db.transaction ['docs'], 'readonly'
       store = txn.objectStore('docs')
 
       req = store.get(doc.slug)
-    req.onsuccess = -> callback(!!req.result)
-    req.onerror = -> callback(false)
+      req.onsuccess = -> fn(!!req.result)
+      req.onerror = -> fn(false)
+      return
     return
 
   load: (entry, onSuccess, onError) ->
-    if @isEnabled()
+    if @useIndexedDB and @_db isnt false
       onError = @loadWithXHR.bind(@, entry, onSuccess, onError)
-      @loadWithIDB(entry, onSuccess, onError)
+      @loadWithIDB entry, onSuccess, onError
     else
-      @loadWithXHR(entry, onSuccess, onError)
+      @loadWithXHR entry, onSuccess, onError
 
   loadWithXHR: (entry, onSuccess, onError) ->
     ajax
@@ -99,7 +118,12 @@ class app.DB
       error: onError
 
   loadWithIDB: (entry, onSuccess, onError) ->
-    txn = @db.transaction [entry.doc.slug], 'readonly'
+    @db (db) ->
+      unless db
+        onError()
+        return
+
+      txn = db.transaction [entry.doc.slug], 'readonly'
       store = txn.objectStore(entry.doc.slug)
 
       req = store.get(entry.path)