本地离线存储localforage
卢开济
关于
HTMl5的sessionStorage和localStorage–灵活使用传送门
localforage 用法类似转载自
API
1）setItem(key, value, successCallback)：创建一个键，参数是键名、键值、回调函数，回调函数的参数是对应的键值。
// Unlike localStorage, you can store non-strings.
localforage.setItem('my array', [1, 2, 'three']).then(function(value) {
// This will output `1`.
console.log(value[0]);
}).catch(function(err) {
// This code runs if there were any errors
console.log(err);
});
2）getItem(key, successCallback):获取数据并使用回调函数
localforage.getItem('somekey', function(err, value) {
// Run this code once the value has been
// loaded from the offline store.
console.log(value);
});
3）removeItem(key, successCallback)：移除对应的键
localforage.removeItem('somekey').then(function() {
// Run this code once the key has been removed.
console.log('Key is cleared!');
}).catch(function(err) {
// This code runs if there were any errors
console.log(err);
});
4）clear(successCallback)：清除所有键。
localforage.clear().then(function() {
// Run this code once the database has been entirely deleted.
console.log('Database is now empty.');
}).catch(function(err) {
// This code runs if there were any errors
console.log(err);
});
5）length(successCallback)：获得离线存储的总的键数。
localforage.length().then(function(numberOfKeys) {
// Outputs the length of the database.
console.log(numberOfKeys);
}).catch(function(err) {
// This code runs if there were any errors
console.log(err);
});
6）key(keyIndex, successCallback)：根据键索引得到键值。
7）keys(successCallback)：得到所有的键索引。
8）iterate(iteratorCallback, successCallback)：对数据库中的每一个键值对调用回调函数，回调函数的参数分别是键值、键索引、迭代次数（基于1）。
// The same code, but using ES6 Promises.
localforage.iterate(function(value, key, iterationNumber) {
// Resulting key/value pair -- this callback
// will be executed for every item in the
// database.
console.log([key, value]);
}).then(function() {
console.log('Iteration has completed');
}).catch(function(err) {
// This code runs if there were any errors
console.log(err);
});
或许并不一定要迭代所有的键值对，此时只要返回一个非undefined类型值，就可以提前结束迭代，这个返回值会作为successCallback的参数。这个方法有点问题，返回的值不太对：
<!DOCTYPE html>
<html>
<head>
<title>Listing 2.1</title>
<script type="text/javascript" src="https://raw.githubusercontent.com/mozilla/localForage/master/dist/localforage.min.js"> </script>
<script type="text/javascript">
localforage.setItem('array', [1, 2,'three']);
localforage.setItem('string', 'people');
localforage.setItem('number1', 5);
localforage.setItem('number2', 6);
localforage.iterate(function(value, key, iterationNumber) {
if (iterationNumber < 2) {
console.log([key, value]);
} else {
return [key, value];
}
}).then(function(result) {
console.log('Iteration has completed at '+ result);
}).catch(function(err) {
console.log(err);
});
</script>
</head>
<body>
</body>
</html>
前面提到，localForage在默认情况下会优先采用使用IDB、WebSQL、localStorage进行后台存储，但是可以通过setDriver()进行后台设置，如果设置的机制在当前浏览器并不支持，则还是按照默认选择。
setDriver(driverName)/setDriver([driverName, nextDriverName]):设置后台支持机制，参数是localforage.INDEXEDDB、localforage.WEBSQL、localforage.LOCALSTORAGE。github使用前需要下载js 库引用
类似资料：