indexDB Polyfill

localForage

 A Polyfill providing a simple name:value syntax for client-side data storage, which uses IndexedDB in the background, but falls back to WebSQL and then localStorage in browsers that don't support IndexedDB. 

Snippet:

// ## setItem(key, item, successCallback)
//    item is javascript object

// With localForage, we use callbacks:
localforage.setItem('key', 'value', doSomethingElse);

// Or we can use Promises:
localforage.setItem('key', 'value').then(doSomethingElse);

// Unlike localStorage, you can store non-strings.
localforage.setItem('my array', [1, 2, 'three'], function(err, item) {
    // This will output `1`.
    console.log(item[0]);
});

// ## getItem(key, successCallback)
localforage.getItem('somekey', function(err, value) {
    // Run this code once the value has been
    // loaded from the offline store.
    console.log(value);
});
localforage.getItem('somekey').then(function(value) {
    // The same code, but using ES6 Promises.
    console.log(value);
});


// ## remove all item
localforage.clear(function(err) {
    // Run this code once the database has been entirely deleted.
    console.log('Database is now empty.');
});

// ## Get the list of all keys in the datastore.
localforage.keys(function(err, keys) {
    // An array of all the key names.
    console.log(keys);
});

// 

// ## Implement the driver here.
var myCustomDriver = {
    _driver: 'customDriverUniqueName',
    _initStorage: function(options) {
        // Custom implementation here...
    },
    clear: function(callback) {
        // Custom implementation here...
    },
    getItem: function(key, callback) {
        // Custom implementation here...
    },
    key: function(n, callback) {
        // Custom implementation here...
    },
    keys: function(callback) {
        // Custom implementation here...
    },
    length: function(callback) {
        // Custom implementation here...
    },
    removeItem: function(key, callback) {
        // Custom implementation here...
    },
    setItem: function(key, value, callback) {
        // Custom implementation here...
    }
}

// Add the driver to localForage.
localforage.defineDriver(myCustomDriver);

Other ref: zh-TW

• Basic Concepts of IndexedDB
• Using IndexedDB