1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
|
/* -*- Mode: Java; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- /
/* vim: set shiftwidth=2 tabstop=2 autoindent cindent expandtab: */
'use strict';
/**
* This file defines an asynchronous version of the localStorage API, backed by
* an IndexedDB database. It creates a global asyncStorage object that has
* methods like the localStorage object.
*
* To store a value use setItem:
*
* asyncStorage.setItem('key', 'value');
*
* If you want confirmation that the value has been stored, pass a callback
* function as the third argument:
*
* asyncStorage.setItem('key', 'newvalue', function() {
* console.log('new value stored');
* });
*
* To read a value, call getItem(), but note that you must supply a callback
* function that the value will be passed to asynchronously:
*
* asyncStorage.getItem('key', function(value) {
* console.log('The value of key is:', value);
* });
*
* Note that unlike localStorage, asyncStorage does not allow you to store and
* retrieve values by setting and querying properties directly. You cannot just
* write asyncStorage.key; you have to explicitly call setItem() or getItem().
*
* removeItem(), clear(), length(), and key() are like the same-named methods of
* localStorage, but, like getItem() and setItem() they take a callback
* argument.
*
* The asynchronous nature of getItem() makes it tricky to retrieve multiple
* values. But unlike localStorage, asyncStorage does not require the values you
* store to be strings. So if you need to save multiple values and want to
* retrieve them together, in a single asynchronous operation, just group the
* values into a single object. The properties of this object may not include
* DOM elements, but they may include things like Blobs and typed arrays.
*
* Unit tests are in apps/gallery/test/unit/asyncStorage_test.js
*/
this.asyncStorage = (function() {
var DBNAME = 'asyncStorage';
var DBVERSION = 1;
var STORENAME = 'keyvaluepairs';
var db = null;
function withStore(type, f) {
if (db) {
f(db.transaction(STORENAME, type).objectStore(STORENAME));
} else {
var openreq = indexedDB.open(DBNAME, DBVERSION);
openreq.onerror = function withStoreOnError() {
console.error("asyncStorage: can't open database:", openreq.error.name);
};
openreq.onupgradeneeded = function withStoreOnUpgradeNeeded() {
// First time setup: create an empty object store
openreq.result.createObjectStore(STORENAME);
};
openreq.onsuccess = function withStoreOnSuccess() {
db = openreq.result;
f(db.transaction(STORENAME, type).objectStore(STORENAME));
};
}
}
function getItem(key, callback) {
withStore('readonly', function getItemBody(store) {
var req = store.get(key);
req.onsuccess = function getItemOnSuccess() {
var value = req.result;
if (value === undefined)
value = null;
callback(value);
};
req.onerror = function getItemOnError() {
console.error('Error in asyncStorage.getItem(): ', req.error.name);
};
});
}
function setItem(key, value, callback) {
withStore('readwrite', function setItemBody(store) {
var req = store.put(value, key);
if (callback) {
req.onsuccess = function setItemOnSuccess() {
callback();
};
}
req.onerror = function setItemOnError() {
console.error('Error in asyncStorage.setItem(): ', req.error.name);
};
});
}
function removeItem(key, callback) {
withStore('readwrite', function removeItemBody(store) {
var req = store.delete(key);
if (callback) {
req.onsuccess = function removeItemOnSuccess() {
callback();
};
}
req.onerror = function removeItemOnError() {
console.error('Error in asyncStorage.removeItem(): ', req.error.name);
};
});
}
function clear(callback) {
withStore('readwrite', function clearBody(store) {
var req = store.clear();
if (callback) {
req.onsuccess = function clearOnSuccess() {
callback();
};
}
req.onerror = function clearOnError() {
console.error('Error in asyncStorage.clear(): ', req.error.name);
};
});
}
function length(callback) {
withStore('readonly', function lengthBody(store) {
var req = store.count();
req.onsuccess = function lengthOnSuccess() {
callback(req.result);
};
req.onerror = function lengthOnError() {
console.error('Error in asyncStorage.length(): ', req.error.name);
};
});
}
function key(n, callback) {
if (n < 0) {
callback(null);
return;
}
withStore('readonly', function keyBody(store) {
var advanced = false;
var req = store.openCursor();
req.onsuccess = function keyOnSuccess() {
var cursor = req.result;
if (!cursor) {
// this means there weren't enough keys
callback(null);
return;
}
if (n === 0) {
// We have the first key, return it if that's what they wanted
callback(cursor.key);
} else {
if (!advanced) {
// Otherwise, ask the cursor to skip ahead n records
advanced = true;
cursor.advance(n);
} else {
// When we get here, we've got the nth key.
callback(cursor.key);
}
}
};
req.onerror = function keyOnError() {
console.error('Error in asyncStorage.key(): ', req.error.name);
};
});
}
return {
getItem: getItem,
setItem: setItem,
removeItem: removeItem,
clear: clear,
length: length,
key: key
};
}());
|
