Usando IndexedDB

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Este tutorial es una guía sobre el uso de la API asincrona de IndexedDB. Si no le es familiar IndexedDB, por favor consulte Basic Concepts About IndexedDB.

Para la documentación de referencia sobre la API de IndexedDB, vea el artículo IndexedDB y sus subpaginas, que documentan los tipos de objetos usados por IndexedDB, así como los métodos síncronos y asíncronos. 

Patrones Básicos

Los patrones básicos que indexedDB alienta son los siguientes:

1. Abre una base de datos.
2. Crea un objeto de almacenamiento en la base de datos.
3. Inicia una transacción y hace una petición que hace alguna operación de la base de datos, tal como añadir o recuperar datos.
4. Espere a que se complete la operación por la escucha de la clase correcta de eventos DOM .
5. Hace algo con el resultado (El cual puede ser encontrado en el objeto de la petición).

Vale, pero, ahora con estos grandes conceptos en nuestro haber, podemos obtener muchas cosas concretas.

Creando y estructurando el almacenamiento

Porque las especificaciones estan todavía involucradas, las implementaciones actuales de indexedDB se esconde bajo el perfil de los navegadores. Los proveedores de navegadores pueden tener diferentes implementaciones de la API estandar de indexedDB hasta que la especificación se ha solidificado. Pero una vez se alcanzó el consenso en el estandar, los proveedores implementan sin la etiqueta de prefijos. Actualmente algunas implementaciones fueron removidos el prefijo:  Internet Explorer 10, Firefox 16, Chrome 24. Cuando utilizan un prefijo, los navegadores basados en gecko usan el prefijo moz , mientras que los navegadores basados en WebKit usan el prefijo webkit.

Usando una versión experimental de IndexedDB

En caso que usted quiera probar su código en navegadores que todavía usen un prefijo, puede usar el siguiente codigo:  

// En la siguiente linea, puede incluir prefijos de implementacion que quiera probar.
window.indexedDB = window.indexedDB || window.mozIndexedDB || window.webkitIndexedDB || window.msIndexedDB;
// No use "var indexedDB = ..." Si no está en una función.
// Por otra parte, puedes necesitar referencias a algun objeto window.IDB*:
window.IDBTransaction = window.IDBTransaction || window.webkitIDBTransaction || window.msIDBTransaction;
window.IDBKeyRange = window.IDBKeyRange || window.webkitIDBKeyRange || window.msIDBKeyRange;
// (Mozilla nunca ha prefijado estos objetos, por lo tanto no necesitamos window.mozIDB*)

Hay que tener cuidado que las implementaciones que usa el prefijo pueda ser erradas, o imcompletas, o siguiendo una versión antigua de la especificación. Por lo tanto, esta no es recomendada a usar en el codigo de producción. puede ser preferido no soportar un navegador que  que ha reclamado soporte y falle :

if (!window.indexedDB) {
    window.alert("Su navegador no soporta una versión estable de indexedDB.Tal y como las características no serán validas");
}

Abriendo una base de datos

Iniciamos todo el proceso así:

// dejamos abierta nuestra base de datos
var request = window.indexedDB.open("MyTestDatabase", 3);

¿Lo has visto? Abrir una base de datos es igual que cualquier otra operación — solo tienes que (request) "solicitarla".

La solicitud de apertura no es abierta por la base de datos o inicia la transacción de inmediato. La llamada a la función open() retornan unos objetos IDBOpenDBRequest con un resultado (correcto) o valor erróneo que manejas en un evento.  Mas otra función asincronica en indexedDB hace lo mismo - Devolver un objeto IDBRequest con el resultado o error. El resultado para la función de abrir es una instancia de un IDBDatabase.

El segundo parámetro para el método open es la versión de la base de datos. La versión de la base de datos determina el esquema - El almacen de objectos en la base de datos y su estructura. Si la base de datos no existe, es creada por el operador abierto, cuando un evento onupgradeneeded es desencadenado de inmediato, permitiendote proveer una actualización de la estructura en el manejador.     Más sobre esto más adelante en  Actualizando la versión de la base de datos. 

var request = indexedDB.open("MyTestDatabase", 2.4); // Esto no se hace, la versión será redondeada a 2

Generando manipuladores

La primera cosa que usted quiere hacer con la casi totalidad de las peticiones que usted genera es agregar controladores de éxito y de error:

request.onerror = function(event) {
  // Do something with request.errorCode!
};
request.onsuccess = function(event) {
  // Do something with request.result!
};

¿Cuál de las dos funciones, onSuccess () o onerror (), se vuelve a llamar? Si todo tiene éxito, un evento de éxito (es decir, un evento DOM cuya propiedad tipo se establece en el "éxito") se dispara con la solicitud como su objetivo. Una vez que se dispara, la función onSuccess () a petición se activa con el evento de éxito como argumento. De lo contrario, si había algún problema, un evento de error (es decir, un evento DOM cuyo tipo de propiedad se establece en "error") se dispara a petición. Esto desencadena la función onerror () con el evento de error como argumento.

La API IndexedDB está diseñado para minimizar la necesidad de control de errores, por lo que no es probable que veamos muchos eventos de error (al menos, no una vez que estás acostumbrado a la API!). En el caso de la apertura de una base de datos, sin embargo, hay algunas condiciones comunes que generan eventos de error. El problema más probable es que el usuario ha decidido no dar a su aplicación web de permiso para crear una base de datos. Uno de los principales objetivos de diseño de IndexedDB es permitir que grandes cantidades de datos que se almacenan para su uso sin conexión. (Para obtener más información sobre la cantidad de almacenamiento que puede tener para cada navegador, consulte Límites de almacenamiento.)  

Obviamente, los navegadores no quieren permitir alguna red de publicidad o sitio web malicioso para contaminar su ordenador, por lo que los navegadores utilizan para indicar al usuario la primera vez que cualquier aplicación web determinada intenta abrir una IndexedDB para el almacenamiento. El usuario puede optar por permitir o denegar el acceso. Además, el almacenamiento IndexedDB en los modos de privacidad navegadores sólo dura en memoria hasta que la sesión de incógnito está cerrado (modo de navegación privada para el modo de Firefox e Incognito para Chrome, pero en Firefox no está implementado a partir de noviembre 2015 por lo que no puede utilizar IndexedDB en Firefox navegación privada en absoluto).

Ahora, en el supuesto de que el usuario deja su solicitud para crear una base de datos, y que ha recibido un evento de éxito para activar la devolución de llamada de éxito; ¿Que sigue? La solicitud aquí se generó con una llamada a indexedDB.open (), por lo request.result es una instancia de IDBDatabase, y que sin duda quieren ahorrar para más adelante. Su código podría ser algo como esto:

var db;
var request = indexedDB.open("MyTestDatabase");
request.onerror = function(event) {
  alert("Why didn't you allow my web app to use IndexedDB?!");
};
request.onsuccess = function(event) {
  db = request.result;
};

Handling Errors

Como se mencionó anteriormente, los eventos de error de burbujas. Eventos de error se dirigen a la solicitud que generó el error, entonces el evento se propaga a la operación, y, finalmente, con el objeto de base de datos. Si desea evitar la adición de controladores de errores a cada solicitud, en su lugar puede añadir un solo controlador de errores en el objeto de base de datos, así:

db.onerror = function(event) {
  // Generic error handler for all errors targeted at this database's
  // requests!
  alert("Database error: " + event.target.errorCode);
};

Uno de los errores más comunes posibles al abrir una base de datos es VER_ERR. Indica que la versión de la base de datos almacenada en el disco es mayor que la versión que está intentando abrir. Este es un caso de error que siempre debe ser manejado por el gestor de errores.

Creación o actualización de la versión de la base de datos

Cuando se crea una nueva base de datos o aumentar el número de versión de una base de datos existente (mediante la especificación de un número de versión más alto de lo que hizo antes, cuando Cómo abrir una base de datos), el evento onupgradeneeded se activará y un objeto IDBVersionChangeEvent será pasado a ningún controlador de eventos onversionchange establecido en request.result (es decir, db en el ejemplo). En el controlador para el evento upgradeneeded, debe crear los almacenes de objetos necesarios para esta versión de la base de datos:

// This event is only implemented in recent browsers
request.onupgradeneeded = function(event) { 
  var db = event.target.result;

  // Create an objectStore for this database
  var objectStore = db.createObjectStore("name", { keyPath: "myKey" });
};

En este caso, la base de datos ya tendrá las tiendas de objetos de la versión anterior de la base de datos, por lo que no tiene que crear estas tiendas de objetos de nuevo. Sólo es necesario crear nuevos almacenes de objetos, o eliminar las tiendas de objetos de la versión anterior que ya no son necesarios. Si necesita cambiar un almacén de objetos existentes (por ejemplo, para cambiar la ruta de acceso clave), entonces usted debe eliminar el antiguo almacén de objetos y crear de nuevo con las nuevas opciones. (Tenga en cuenta que esto borrará la información en el almacén de objetos Si usted necesita guardar esa información, usted debe leerlo y guardarlo en otro lugar antes de actualizar la base de datos.)

Tratando de crear un almacén de objetos con un nombre que ya existe (o tratando de eliminar un almacén de objetos con un nombre que no existe ya) lanzará un error. Si el evento onupgradeneeded sale con éxito, entonces se activará el manejador onSuccess de la solicitud de base de datos abierta.

Blink / Webkit apoya la versión actual de la especificación, que fue enviado en Chrome y Opera 17+ 23+; IE10 + también lo hace. Otros años o más implementaciones no implementan la versión actual de la especificación, y por lo tanto no son compatibles con el indexedDB.open (nombre, versión) firma .onupgradeneeded todavía. Para obtener más información sobre cómo actualizar la versión de la base de datos en Webkit mayor / Blink, consulte el artículo de referencia IDBDatabase. IDBDatabase.

Estructuración de la base de datos

Now to structure the database. IndexedDB uses object stores rather than tables, and a single database can contain any number of object stores. Whenever a value is stored in an object store, it is associated with a key. There are several different ways that a key can be supplied depending on whether the object store uses a key path or a key generator.

The following table shows the different ways the keys are supplied:

You can also create indices on any object store, provided the object store holds objects, not primitives. An index lets you look up the values stored in an object store using the value of a property of the stored object, rather than the object's key.

Additionally, indexes have the ability to enforce simple constraints on the stored data. By setting the unique flag when creating the index, the index ensures that no two objects are stored with both having the same value for the index's key path. So, for example, if you have an object store which holds a set of people, and you want to ensure that no two people have the same email address, you can use an index with the unique flag set to enforce this.

That may sound confusing, but this simple example should illustrate the concepts. First, we'll define some customer data to use in our example:

// This is what our customer data looks like.
const customerData = [
  { ssn: "444-44-4444", name: "Bill", age: 35, email: "[email protected]" },
  { ssn: "555-55-5555", name: "Donna", age: 32, email: "[email protected]" }
];

Now let's look at creating an IndexedDB to store our data:

const dbName = "the_name";

var request = indexedDB.open(dbName, 2);

request.onerror = function(event) {
  // Handle errors.
};
request.onupgradeneeded = function(event) {
  var db = event.target.result;

  // Create an objectStore to hold information about our customers. We're
  // going to use "ssn" as our key path because it's guaranteed to be
  // unique.
  var objectStore = db.createObjectStore("customers", { keyPath: "ssn" });

  // Create an index to search customers by name. We may have duplicates
  // so we can't use a unique index.
  objectStore.createIndex("name", "name", { unique: false });

  // Create an index to search customers by email. We want to ensure that
  // no two customers have the same email, so use a unique index.
  objectStore.createIndex("email", "email", { unique: true });

  // Use transaction oncomplete to make sure the objectStore creation is 
  // finished before adding data into it.
  objectStore.transaction.oncomplete = function(event) {
    // Store values in the newly created objectStore.
    var customerObjectStore = db.transaction("customers", "readwrite").objectStore("customers");
    for (var i in customerData) {
      customerObjectStore.add(customerData[i]);
    }
  }
};

As indicated previously, onupgradeneeded is the only place where you can alter the structure of the database. In it, you can create and delete object stores and build and remove indices.

We've also asked for an index named "name" that looks at the name property of the stored objects. As with createObjectStore(), createIndex() takes an optional options object that refines the type of index that you want to create. Adding objects that don't have a name property still succeeds, but the objects won't appear in the "name" index.

We can now retrieve the stored customer objects using their ssn from the object store directly, or using their name by using the index. To learn how this is done, see the section on using an index.

El uso de un generador de claves

Setting up an autoIncrement flag when creating the object store would enable the key generator for that object store. By default this flag is not set.

With the key generator, the key would be generated automatically as you add the value to the object store. The current number of a key generator is always set to 1 when the object store for that key generator is first created. Basically the newly auto-generated key is increased by 1 based on the previous key. The current number for a key generator never decreases, other than as a result of database operations being reverted, for example, the database transcation is aborted. Therefore deleting a record or even clearing all records from an object store never affects the object store's key generator.

We can create another object store with the key generator as below:

// Open the indexedDB.
var request = indexedDB.open(dbName, 3);

request.onupgradeneeded = function (event) {

    var db = event.target.result;

    // Create another object store called "names" with the autoIncrement flag set as true.    
    var objStore = db.createObjectStore("names", { autoIncrement : true });

    // Because the "names" object store has the key generator, the key for the name value is generated automatically.
    // The added records would be like:
    // key : 1 => value : "Bill"
    // key : 2 => value : "Donna"
    for (var i in customerData) {
        objStore.add(customerData[i].name);
    }
}

For more details about the key generator, please see "W3C Key Generators".

Añadir, recuperación y eliminación de datos

Before you can do anything with your new database, you need to start a transaction. Transactions come from the database object, and you have to specify which object stores you want the transaction to span. Once you are inside the transaction, you can access the object stores that hold your data and make your requests. Next, you need to decide if you're going to make changes to the database or if you just need to read from it. Transactions have three available modes: readonly, readwrite, and versionchange.

To change the "schema" or structure of the database—which involves creating or deleting object stores or indexes—the transaction must be in versionchange mode. This transaction is opened by calling the IDBFactory.open method with a version specified. (In WebKit browsers, which have not implemented the latest specifcation, the IDBFactory.open method takes only one parameter, the name of the database; then you must call IDBVersionChangeRequest.setVersion to establish the versionchange transaction.)

To read the records of an existing object store, the transaction can either be in readonly or readwrite mode. To make changes to an existing object store, the transaction must be in readwrite mode. You open such transactions with IDBDatabase.transaction. The method accepts two parameters: the storeNames (the scope, defined as an array of object stores that you want to access) and the mode (readonly or readwrite) for the transaction. The method returns a transaction object containing the IDBIndex.objectStore method, which you can use to access your object store. By default, where no mode is specified, transactions open in readonly mode.

You can speed up data access by using the right scope and mode in the transaction. Here are a couple of tips:

• When defining the scope, specify only the object stores you need. This way, you can run multiple transactions with non-overlapping scopes concurrently.
• Only specify a readwrite transaction mode when necessary. You can concurrently run multiple readonly transactions with overlapping scopes, but you can have only one readwrite transaction for an object store. To learn more, see the definition for transactions in the Basic Concepts article.

Agregar datos a la base de datos

If you've just created a database, then you probably want to write to it. Here's what that looks like:

var transaction = db.transaction(["customers"], "readwrite");
// Note: Older experimental implementations use the deprecated constant IDBTransaction.READ_WRITE instead of "readwrite".
// In case you want to support such an implementation, you can write: 
// var transaction = db.transaction(["customers"], IDBTransaction.READ_WRITE);

The transaction() function takes two arguments (though one is optional) and returns a transaction object. The first argument is a list of object stores that the transaction will span. You can pass an empty array if you want the transaction to span all object stores, but don't do it because the spec says an empty array should generate an InvalidAccessError. If you don't specify anything for the second argument, you get a read-only transaction. Since you want to write to it here you need to pass the "readwrite" flag.

Now that you have a transaction you need to understand its lifetime. Transactions are tied very closely to the event loop. If you make a transaction and return to the event loop without using it then the transaction will become inactive. The only way to keep the transaction active is to make a request on it. When the request is finished you'll get a DOM event and, assuming that the request succeeded, you'll have another opportunity to extend the transaction during that callback. If you return to the event loop without extending the transaction then it will become inactive, and so on. As long as there are pending requests the transaction remains active. Transaction lifetimes are really very simple but it might take a little time to get used to. A few more examples will help, too. If you start seeing TRANSACTION_INACTIVE_ERR error codes then you've messed something up.

Transactions can receive DOM events of three different types: error, abort, and complete. We've talked about the way that error events bubble, so a transaction receives error events from any requests that are generated from it. A more subtle point here is that the default behavior of an error is to abort the transaction in which it occurred. Unless you handle the error by first calling preventDefault() on the error event then doing something else, the entire transaction is rolled back. This design forces you to think about and handle errors, but you can always add a catchall error handler to the database if fine-grained error handling is too cumbersome. If you don't handle an error event or if you call abort() on the transaction, then the transaction is rolled back and an abort event is fired on the transaction. Otherwise, after all pending requests have completed, you'll get a complete event. If you're doing lots of database operations, then tracking the transaction rather than individual requests can certainly aid your sanity.

Now that you have a transaction, you'll need to get the object store from it. Transactions only let you have an object store that you specified when creating the transaction. Then you can add all the data you need.

// Do something when all the data is added to the database.
transaction.oncomplete = function(event) {
  alert("All done!");
};

transaction.onerror = function(event) {
  // Don't forget to handle errors!
};

var objectStore = transaction.objectStore("customers");
for (var i in customerData) {
  var request = objectStore.add(customerData[i]);
  request.onsuccess = function(event) {
    // event.target.result == customerData[i].ssn;
  };
}

The result of a request generated from a call to add() is the key of the value that was added. So in this case, it should equal the ssn property of the object that was added, since the object store uses the ssn property for the key path. Note that the add() function requires that no object already be in the database with the same key. If you're trying to modify an existing entry, or you don't care if one exists already, you can use the put() function, as shown below in the Updating an entry in the database section.

Extracción de datos de la base de datos

Removing data is very similar:

var request = db.transaction(["customers"], "readwrite")
                .objectStore("customers")
                .delete("444-44-4444");
request.onsuccess = function(event) {
  // It's gone!
};

Obtener datos de la base de datos

Now that the database has some info in it, you can retrieve it in several ways. First, the simple get(). You need to provide the key to retrieve the value, like so:

var transaction = db.transaction(["customers"]);
var objectStore = transaction.objectStore("customers");
var request = objectStore.get("444-44-4444");
request.onerror = function(event) {
  // Handle errors!
};
request.onsuccess = function(event) {
  // Do something with the request.result!
  alert("Name for SSN 444-44-4444 is " + request.result.name);
};

That's a lot of code for a "simple" retrieval. Here's how you can shorten it up a bit, assuming that you handle errors at the database level:

db.transaction("customers").objectStore("customers").get("444-44-4444").onsuccess = function(event) {
  alert("Name for SSN 444-44-4444 is " + event.target.result.name);
};

See how this works? Since there's only one object store, you can avoid passing a list of object stores you need in your transaction and just pass the name as a string. Also, you're only reading from the database, so you don't need a "readwrite" transaction. Calling transaction() with no mode specified gives you a "readonly" transaction. Another subtlety here is that you don't actually save the request object to a variable. Since the DOM event has the request as its target you can use the event to get to the result property.

Actualización de una entrada en la base de datos

Now we've retrieved some data, updating it and inserting it back into the IndexedDB is pretty simple. Let's update the previous example somewhat:

var objectStore = db.transaction(["customers"], "readwrite").objectStore("customers");
var request = objectStore.get("444-44-4444");
request.onerror = function(event) {
  // Handle errors!
};
request.onsuccess = function(event) {
  // Get the old value that we want to update
  var data = request.result;
  
  // update the value(s) in the object that you want to change
  data.age = 42;

  // Put this updated object back into the database.
  var requestUpdate = objectStore.put(data);
   requestUpdate.onerror = function(event) {
     // Do something with the error
   };
   requestUpdate.onsuccess = function(event) {
     // Success - the data is updated!
   };
};

So here we're creating an objectStore and requesting a customer record out of it, identified by its ssn value (444-44-4444). We then put the result of that request in a variable (data), update the age property of this object, then create a second request (requestUpdate) to put the customer record back into the objectStore, overwriting the previous value.

El uso de un cursor

Using get() requires that you know which key you want to retrieve. If you want to step through all the values in your object store, then you can use a cursor. Here's what it looks like:

var objectStore = db.transaction("customers").objectStore("customers");

objectStore.openCursor().onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    alert("Name for SSN " + cursor.key + " is " + cursor.value.name);
    cursor.continue();
  }
  else {
    alert("No more entries!");
  }
};

The openCursor() function takes several arguments. First, you can limit the range of items that are retrieved by using a key range object that we'll get to in a minute. Second, you can specify the direction that you want to iterate. In the above example, we're iterating over all objects in ascending order. The success callback for cursors is a little special. The cursor object itself is the result of the request (above we're using the shorthand, so it's event.target.result). Then the actual key and value can be found on the key and value properties of the cursor object. If you want to keep going, then you have to call continue() on the cursor. When you've reached the end of the data (or if there were no entries that matched your openCursor() request) you still get a success callback, but the result property is undefined.

One common pattern with cursors is to retrieve all objects in an object store and add them to an array, like this:

var customers = [];

objectStore.openCursor().onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    customers.push(cursor.value);
    cursor.continue();
  }
  else {
    alert("Got all customers: " + customers);
  }
};

objectStore.getAll().onsuccess = function(event) {
  alert("Got all customers: " + event.target.result);
};

El uso de un índice

Storing customer data using the SSN as a key is logical since the SSN uniquely identifies an individual. (Whether this is a good idea for privacy is a different question, and outside the scope of this article.) If you need to look up a customer by name, however, you'll need to iterate over every SSN in the database until you find the right one. Searching in this fashion would be very slow, so instead you can use an index.

var index = objectStore.index("name");
index.get("Donna").onsuccess = function(event) {
  alert("Donna's SSN is " + event.target.result.ssn);
};

The "name" cursor isn't unique, so there could be more than one entry with the name set to "Donna". In that case you always get the one with the lowest key value.

If you need to access all the entries with a given name you can use a cursor. You can open two different types of cursors on indexes. A normal cursor maps the index property to the object in the object store. A key cursor maps the index property to the key used to store the object in the object store. The differences are illustrated here:

// Using a normal cursor to grab whole customer record objects
index.openCursor().onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    // cursor.key is a name, like "Bill", and cursor.value is the whole object.
    alert("Name: " + cursor.key + ", SSN: " + cursor.value.ssn + ", email: " + cursor.value.email);
    cursor.continue();
  }
};

// Using a key cursor to grab customer record object keys
index.openKeyCursor().onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    // cursor.key is a name, like "Bill", and cursor.value is the SSN.
    // No way to directly get the rest of the stored object.
    alert("Name: " + cursor.key + ", SSN: " + cursor.value);
    cursor.continue();
  }
};

Especificación de la gama y la dirección de los cursores

If you would like to limit the range of values you see in a cursor, you can use an IDBKeyRange object and pass it as the first argument to openCursor() or openKeyCursor(). You can make a key range that only allows a single key, or one that has a lower or upper bound, or one that has both a lower and upper bound. The bound may be "closed" (i.e., the key range includes the given value(s)) or "open" (i.e., the key range does not include the given value(s)). Here's how it works:

// Only match "Donna"
var singleKeyRange = IDBKeyRange.only("Donna");

// Match anything past "Bill", including "Bill"
var lowerBoundKeyRange = IDBKeyRange.lowerBound("Bill");

// Match anything past "Bill", but don't include "Bill"
var lowerBoundOpenKeyRange = IDBKeyRange.lowerBound("Bill", true);

// Match anything up to, but not including, "Donna"
var upperBoundOpenKeyRange = IDBKeyRange.upperBound("Donna", true);

// Match anything between "Bill" and "Donna", but not including "Donna"
var boundKeyRange = IDBKeyRange.bound("Bill", "Donna", false, true);

// To use one of the key ranges, pass it in as the first argument of openCursor()/openKeyCursor()
index.openCursor(boundKeyRange).onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    // Do something with the matches.
    cursor.continue();
  }
};

Sometimes you may want to iterate in descending order rather than in ascending order (the default direction for all cursors). Switching direction is accomplished by passing prev to the openCursor() function as the second argument:

objectStore.openCursor(boundKeyRange, "prev").onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    // Do something with the entries.
    cursor.continue();
  }
};

If you just want to specify a change of direction but not constrain the results shown, you can just pass in null as the first argument:

objectStore.openCursor(null, "prev").onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    // Do something with the entries.
    cursor.continue();
  }
};

Since the "name" index isn't unique, there might be multiple entries where name is the same. Note that such a situation cannot occur with object stores since the key must always be unique. If you wish to filter out duplicates during cursor iteration over indexes, you can pass nextunique (or prevunique if you're going backwards) as the direction parameter. When nextunique or prevunique is used, the entry with the lowest key is always the one returned.

index.openKeyCursor(null, "nextunique").onsuccess = function(event) {
  var cursor = event.target.result;
  if (cursor) {
    // Do something with the entries.
    cursor.continue();
  }
};

Please see "IDBCursor Constants" for the valid direction arguments.

Cambios Versión mientras que una aplicación web está abierto en otra pestaña

When your web app changes in such a way that a version change is required for your database, you need to consider what happens if the user has the old version of your app open in one tab and then loads the new version of your app in another. When you call open() with a greater version than the actual version of the database, all other open databases must explicitly acknowledge the request before you can start making changes to the database (an onblocked event is fired until tey are closed or reloaded). Here's how it works:

var openReq = mozIndexedDB.open("MyTestDatabase", 2);

openReq.onblocked = function(event) {
  // If some other tab is loaded with the database, then it needs to be closed
  // before we can proceed.
  alert("Please close all other tabs with this site open!");
};
  
openReq.onupgradeneeded = function(event) {
  // All other databases have been closed. Set everything up.
  db.createObjectStore(/* ... */);
  useDatabase(db);
}  
  
openReq.onsuccess = function(event) {
  var db = event.target.result;
  useDatabase(db);
  return;
}

function useDatabase(db) {
  // Make sure to add a handler to be notified if another page requests a version
  // change. We must close the database. This allows the other page to upgrade the database.
  // If you don't do this then the upgrade won't happen until the user closes the tab.
  db.onversionchange = function(event) {
    db.close();
    alert("A new version of this page is ready. Please reload!");
  };

  // Do stuff with the database.
}

Seguridad

IndexedDB uses the same-origin principle, which means that it ties the store to the origin of the site that creates it (typically, this is the site domain or subdomain), so it cannot be accessed by any other origin.

It's important to note that IndexedDB doesn't work for content loaded into a frame from another site (either <frame> or <iframe>. This is a security and privacy measure and can be considered analogous the blocking of third-party cookies. For more details, see bug 595307.

Warning About Browser Shutdown

When the browser shuts down (e.g., when the user selects Exit or clicks the Close button), any pending IndexedDB transactions are (silently) aborted — they will not complete, and they will not trigger the error handler. Since the user can exit the browser at any time, this means that you cannot rely upon any particular transaction to complete or to know that it did not complete. There are several implications of this behavior.

First, you should take care to always leave your database in a consistent state at the end of every transaction. For example, suppose that you are using IndexedDB to store a list of items that you allow the user to edit. You save the list after the edit by clearing the object store and then writing out the new list. If you clear the object store in one transaction and write the new list in another transaction, there is a danger that the browser will close after the clear but before the write, leaving you with an empty database. To avoid this, you should combine the clear and the write into a single transaction. 

Second, you should never tie database transactions to unload events. If the unload event is triggered by the browser closing, any transactions created in the unload event handler will never complete. An intuitive approach to maintaining some information across browser sessions is to read it from the database when the browser (or a particular page) is opened, update it as the user interacts with the browser, and then save it to the database when the browser (or page) closes. However, this will not work. The database transactions will be created in the unload event handler, but because they are asynchronous they will be aborted before they can execute.

In fact, there is no way to guarantee that IndexedDB transactions will complete, even with normal browser shutdown. See bug 870645.

Full IndexedDB example

HTML Content

<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>    

    <h1>IndexedDB Demo: storing blobs, e-publication example</h1>
    <div class="note">
      <p>
        Works and tested with:
      </p>
      <div id="compat">
      </div>
    </div>

    <div id="msg">
    </div>

    <form id="register-form">
      <table>
        <tbody>
          <tr>
            <td>
              <label for="pub-title" class="required">
                Title:
              </label>
            </td>
            <td>
              <input type="text" id="pub-title" name="pub-title" />
            </td>
          </tr>
          <tr>
            <td>
              <label for="pub-biblioid" class="required">
                Bibliographic ID:<br/>
                <span class="note">(ISBN, ISSN, etc.)</span>
              </label>
            </td>
            <td>
              <input type="text" id="pub-biblioid" name="pub-biblioid"/>
            </td>
          </tr>
          <tr>
            <td>
              <label for="pub-year">
                Year:
              </label>
            </td>
            <td>
              <input type="number" id="pub-year" name="pub-year" />
            </td>
          </tr>
        </tbody>
        <tbody>
          <tr>
            <td>
              <label for="pub-file">
                File image:
              </label>
            </td>
            <td>
              <input type="file" id="pub-file"/>
            </td>
          </tr>
          <tr>
            <td>
              <label for="pub-file-url">
                Online-file image URL:<br/>
                <span class="note">(same origin URL)</span>
              </label>
            </td>
            <td>
              <input type="text" id="pub-file-url" name="pub-file-url"/>
            </td>
          </tr>
        </tbody>
      </table>

      <div class="button-pane">
        <input type="button" id="add-button" value="Add Publication" />
        <input type="reset" id="register-form-reset"/>
      </div>
    </form>

    <form id="delete-form">
      <table>
        <tbody>
          <tr>
            <td>
              <label for="pub-biblioid-to-delete">
                Bibliographic ID:<br/>
                <span class="note">(ISBN, ISSN, etc.)</span>
              </label>
            </td>
            <td>
              <input type="text" id="pub-biblioid-to-delete"
                     name="pub-biblioid-to-delete" />
            </td>
          </tr>
          <tr>
            <td>
              <label for="key-to-delete">
                Key:<br/>
                <span class="note">(for example 1, 2, 3, etc.)</span>
              </label>
            </td>
            <td>
              <input type="text" id="key-to-delete"
                     name="key-to-delete" />
            </td>
          </tr>
        </tbody>
      </table>
      <div class="button-pane">
        <input type="button" id="delete-button" value="Delete Publication" />
        <input type="button" id="clear-store-button"
               value="Clear the whole store" class="destructive" />
      </div>
    </form>

    <form id="search-form">
      <div class="button-pane">
        <input type="button" id="search-list-button"
               value="List database content" />
      </div>
    </form>

    <div>
      <div id="pub-msg">
      </div>
      <div id="pub-viewer">
      </div>
      <ul id="pub-list">
      </ul>
    </div>

CSS Content

body {
  font-size: 0.8em;
  font-family: Sans-Serif;
}

form {
  background-color: #cccccc;
  border-radius: 0.3em;
  display: inline-block;
  margin-bottom: 0.5em;
  padding: 1em;
}

table {
  border-collapse: collapse;
}

input {
  padding: 0.3em;
  border-color: #cccccc;
  border-radius: 0.3em;
}

.required:after {
  content: "*";
  color: red;
}

.button-pane {
  margin-top: 1em;
}

#pub-viewer {
  float: right;
  width: 48%;
  height: 20em;
  border: solid #d092ff 0.1em;
}
#pub-viewer iframe {
  width: 100%;
  height: 100%;
}

#pub-list {
  width: 46%;
  background-color: #eeeeee;
  border-radius: 0.3em;
}
#pub-list li {
  padding-top: 0.5em;
  padding-bottom: 0.5em;
  padding-right: 0.5em;
}

#msg {
  margin-bottom: 1em;
}

.action-success {
  padding: 0.5em;
  color: #00d21e;
  background-color: #eeeeee;
  border-radius: 0.2em;
}

.action-failure {
  padding: 0.5em;
  color: #ff1408;
  background-color: #eeeeee;
  border-radius: 0.2em;
}

.note {
  font-size: smaller;
}

.destructive {
  background-color: orange;
}
.destructive:hover {
  background-color: #ff8000;
}
.destructive:active {
  background-color: red;
}

JavaScript Content

(function () {
  var COMPAT_ENVS = [
    ['Firefox', ">= 16.0"],
    ['Google Chrome',
     ">= 24.0 (you may need to get Google Chrome Canary), NO Blob storage support"]
  ];
  var compat = $('#compat');
  compat.empty();
  compat.append('<ul id="compat-list"></ul>');
  COMPAT_ENVS.forEach(function(val, idx, array) {
    $('#compat-list').append('<li>' + val[0] + ': ' + val[1] + '</li>');
  });

  const DB_NAME = 'mdn-demo-indexeddb-epublications';
  const DB_VERSION = 1; // Use a long long for this value (don't use a float)
  const DB_STORE_NAME = 'publications';

  var db;

  // Used to keep track of which view is displayed to avoid uselessly reloading it
  var current_view_pub_key;

  function openDb() {
    console.log("openDb ...");
    var req = indexedDB.open(DB_NAME, DB_VERSION);
    req.onsuccess = function (evt) {
      // Better use "this" than "req" to get the result to avoid problems with
      // garbage collection.
      // db = req.result;
      db = this.result;
      console.log("openDb DONE");
    };
    req.onerror = function (evt) {
      console.error("openDb:", evt.target.errorCode);
    };

    req.onupgradeneeded = function (evt) {
      console.log("openDb.onupgradeneeded");
      var store = evt.currentTarget.result.createObjectStore(
        DB_STORE_NAME, { keyPath: 'id', autoIncrement: true });

      store.createIndex('biblioid', 'biblioid', { unique: true });
      store.createIndex('title', 'title', { unique: false });
      store.createIndex('year', 'year', { unique: false });
    };
  }

  /**
   * @param {string} store_name
   * @param {string} mode either "readonly" or "readwrite"
   */
  function getObjectStore(store_name, mode) {
    var tx = db.transaction(store_name, mode);
    return tx.objectStore(store_name);
  }

  function clearObjectStore(store_name) {
    var store = getObjectStore(DB_STORE_NAME, 'readwrite');
    var req = store.clear();
    req.onsuccess = function(evt) {
      displayActionSuccess("Store cleared");
      displayPubList(store);
    };
    req.onerror = function (evt) {
      console.error("clearObjectStore:", evt.target.errorCode);
      displayActionFailure(this.error);
    };
  }

  function getBlob(key, store, success_callback) {
    var req = store.get(key);
    req.onsuccess = function(evt) {
      var value = evt.target.result;
      if (value)
        success_callback(value.blob);
    };
  }

  /**
   * @param {IDBObjectStore=} store
   */
  function displayPubList(store) {
    console.log("displayPubList");

    if (typeof store == 'undefined')
      store = getObjectStore(DB_STORE_NAME, 'readonly');

    var pub_msg = $('#pub-msg');
    pub_msg.empty();
    var pub_list = $('#pub-list');
    pub_list.empty();
    // Resetting the iframe so that it doesn't display previous content
    newViewerFrame();

    var req;
    req = store.count();
    // Requests are executed in the order in which they were made against the
    // transaction, and their results are returned in the same order.
    // Thus the count text below will be displayed before the actual pub list
    // (not that it is algorithmically important in this case).
    req.onsuccess = function(evt) {
      pub_msg.append('<p>There are <strong>' + evt.target.result +
                     '</strong> record(s) in the object store.</p>');
    };
    req.onerror = function(evt) {
      console.error("add error", this.error);
      displayActionFailure(this.error);
    };

    var i = 0;
    req = store.openCursor();
    req.onsuccess = function(evt) {
      var cursor = evt.target.result;

      // If the cursor is pointing at something, ask for the data
      if (cursor) {
        console.log("displayPubList cursor:", cursor);
        req = store.get(cursor.key);
        req.onsuccess = function (evt) {
          var value = evt.target.result;
          var list_item = $('<li>' +
                            '[' + cursor.key + '] ' +
                            '(biblioid: ' + value.biblioid + ') ' +
                            value.title +
                            '</li>');
          if (value.year != null)
            list_item.append(' - ' + value.year);

          if (value.hasOwnProperty('blob') &&
              typeof value.blob != 'undefined') {
            var link = $('<a href="' + cursor.key + '">File</a>');
            link.on('click', function() { return false; });
            link.on('mouseenter', function(evt) {
                      setInViewer(evt.target.getAttribute('href')); });
            list_item.append(' / ');
            list_item.append(link);
          } else {
            list_item.append(" / No attached file");
          }
          pub_list.append(list_item);
        };

        // Move on to the next object in store
        cursor.continue();

        // This counter serves only to create distinct ids
        i++;
      } else {
        console.log("No more entries");
      }
    };
  }

  function newViewerFrame() {
    var viewer = $('#pub-viewer');
    viewer.empty();
    var iframe = $('<iframe />');
    viewer.append(iframe);
    return iframe;
  }

  function setInViewer(key) {
    console.log("setInViewer:", arguments);
    key = Number(key);
    if (key == current_view_pub_key)
      return;

    current_view_pub_key = key;

    var store = getObjectStore(DB_STORE_NAME, 'readonly');
    getBlob(key, store, function(blob) {
      console.log("setInViewer blob:", blob);
      var iframe = newViewerFrame();

      // It is not possible to set a direct link to the
      // blob to provide a mean to directly download it.
      if (blob.type == 'text/html') {
        var reader = new FileReader();
        reader.onload = (function(evt) {
          var html = evt.target.result;
          iframe.load(function() {
            $(this).contents().find('html').html(html);
          });
        });
        reader.readAsText(blob);
      } else if (blob.type.indexOf('image/') == 0) {
        iframe.load(function() {
          var img_id = 'image-' + key;
          var img = $('<img id="' + img_id + '"/>');
          $(this).contents().find('body').html(img);
          var obj_url = window.URL.createObjectURL(blob);
          $(this).contents().find('#' + img_id).attr('src', obj_url);
          window.URL.revokeObjectURL(obj_url);
        });
      } else if (blob.type == 'application/pdf') {
        $('*').css('cursor', 'wait');
        var obj_url = window.URL.createObjectURL(blob);
        iframe.load(function() {
          $('*').css('cursor', 'auto');
        });
        iframe.attr('src', obj_url);
        window.URL.revokeObjectURL(obj_url);
      } else {
        iframe.load(function() {
          $(this).contents().find('body').html("No view available");
        });
      }

    });
  }

  /**
   * @param {string} biblioid
   * @param {string} title
   * @param {number} year
   * @param {string} url the URL of the image to download and store in the local
   *   IndexedDB database. The resource behind this URL is subjected to the
   *   "Same origin policy", thus for this method to work, the URL must come from
   *   the same origin as the web site/app this code is deployed on.
   */
  function addPublicationFromUrl(biblioid, title, year, url) {
    console.log("addPublicationFromUrl:", arguments);

    var xhr = new XMLHttpRequest();
    xhr.open('GET', url, true);
    // Setting the wanted responseType to "blob"
    // https://www.w3.org/TR/XMLHttpRequest2/#the-response-attribute
    xhr.responseType = 'blob';
    xhr.onload = function (evt) {
                           if (xhr.status == 200) {
                             console.log("Blob retrieved");
                             var blob = xhr.response;
                             console.log("Blob:", blob);
                             addPublication(biblioid, title, year, blob);
                           } else {
                             console.error("addPublicationFromUrl error:",
                                           xhr.responseText, xhr.status);
                           }
                         };
    xhr.send();

    // We can't use jQuery here because as of jQuery 1.8.3 the new "blob"
    // responseType is not handled.
    // https://bugs.jquery.com/ticket/11461
    // https://bugs.jquery.com/ticket/7248
    // $.ajax({
    //   url: url,
    //   type: 'GET',
    //   xhrFields: { responseType: 'blob' },
    //   success: function(data, textStatus, jqXHR) {
    //     console.log("Blob retrieved");
    //     console.log("Blob:", data);
    //     // addPublication(biblioid, title, year, data);
    //   },
    //   error: function(jqXHR, textStatus, errorThrown) {
    //     console.error(errorThrown);
    //     displayActionFailure("Error during blob retrieval");
    //   }
    // });
  }

  /**
   * @param {string} biblioid
   * @param {string} title
   * @param {number} year
   * @param {Blob=} blob
   */
  function addPublication(biblioid, title, year, blob) {
    console.log("addPublication arguments:", arguments);
    var obj = { biblioid: biblioid, title: title, year: year };
    if (typeof blob != 'undefined')
      obj.blob = blob;

    var store = getObjectStore(DB_STORE_NAME, 'readwrite');
    var req;
    try {
      req = store.add(obj);
    } catch (e) {
      if (e.name == 'DataCloneError')
        displayActionFailure("This engine doesn't know how to clone a Blob, " +
                             "use Firefox");
      throw e;
    }
    req.onsuccess = function (evt) {
      console.log("Insertion in DB successful");
      displayActionSuccess();
      displayPubList(store);
    };
    req.onerror = function() {
      console.error("addPublication error", this.error);
      displayActionFailure(this.error);
    };
  }

  /**
   * @param {string} biblioid
   */
  function deletePublicationFromBib(biblioid) {
    console.log("deletePublication:", arguments);
    var store = getObjectStore(DB_STORE_NAME, 'readwrite');
    var req = store.index('biblioid');
    req.get(biblioid).onsuccess = function(evt) {
      if (typeof evt.target.result == 'undefined') {
        displayActionFailure("No matching record found");
        return;
      }
      deletePublication(evt.target.result.id, store);
    };
    req.onerror = function (evt) {
      console.error("deletePublicationFromBib:", evt.target.errorCode);
    };
  }

  /**
   * @param {number} key
   * @param {IDBObjectStore=} store
   */
  function deletePublication(key, store) {
    console.log("deletePublication:", arguments);

    if (typeof store == 'undefined')
      store = getObjectStore(DB_STORE_NAME, 'readwrite');

    // As per spec https://www.w3.org/TR/IndexedDB/#object-store-deletion-operation
    // the result of the Object Store Deletion Operation algorithm is
    // undefined, so it's not possible to know if some records were actually
    // deleted by looking at the request result.
    var req = store.get(key);
    req.onsuccess = function(evt) {
      var record = evt.target.result;
      console.log("record:", record);
      if (typeof record == 'undefined') {
        displayActionFailure("No matching record found");
        return;
      }
      // Warning: The exact same key used for creation needs to be passed for
      // the deletion. If the key was a Number for creation, then it needs to
      // be a Number for deletion.
      req = store.delete(key);
      req.onsuccess = function(evt) {
        console.log("evt:", evt);
        console.log("evt.target:", evt.target);
        console.log("evt.target.result:", evt.target.result);
        console.log("delete successful");
        displayActionSuccess("Deletion successful");
        displayPubList(store);
      };
      req.onerror = function (evt) {
        console.error("deletePublication:", evt.target.errorCode);
      };
    };
    req.onerror = function (evt) {
      console.error("deletePublication:", evt.target.errorCode);
      };
  }

  function displayActionSuccess(msg) {
    msg = typeof msg != 'undefined' ? "Success: " + msg : "Success";
    $('#msg').html('<span class="action-success">' + msg + '</span>');
  }
  function displayActionFailure(msg) {
    msg = typeof msg != 'undefined' ? "Failure: " + msg : "Failure";
    $('#msg').html('<span class="action-failure">' + msg + '</span>');
  }
  function resetActionStatus() {
    console.log("resetActionStatus ...");
    $('#msg').empty();
    console.log("resetActionStatus DONE");
  }

  function addEventListeners() {
    console.log("addEventListeners");

    $('#register-form-reset').click(function(evt) {
      resetActionStatus();
    });

    $('#add-button').click(function(evt) {
      console.log("add ...");
      var title = $('#pub-title').val();
      var biblioid = $('#pub-biblioid').val();
      if (!title || !biblioid) {
        displayActionFailure("Required field(s) missing");
        return;
      }
      var year = $('#pub-year').val();
      if (year != '') {
        // Better use Number.isInteger if the engine has EcmaScript 6
        if (isNaN(year))  {
          displayActionFailure("Invalid year");
          return;
        }
        year = Number(year);
      } else {
        year = null;
      }

      var file_input = $('#pub-file');
      var selected_file = file_input.get(0).files[0];
      console.log("selected_file:", selected_file);
      // Keeping a reference on how to reset the file input in the UI once we
      // have its value, but instead of doing that we rather use a "reset" type
      // input in the HTML form.
      //file_input.val(null);
      var file_url = $('#pub-file-url').val();
      if (selected_file) {
        addPublication(biblioid, title, year, selected_file);
      } else if (file_url) {
        addPublicationFromUrl(biblioid, title, year, file_url);
      } else {
        addPublication(biblioid, title, year);
      }

    });

    $('#delete-button').click(function(evt) {
      console.log("delete ...");
      var biblioid = $('#pub-biblioid-to-delete').val();
      var key = $('#key-to-delete').val();

      if (biblioid != '') {
        deletePublicationFromBib(biblioid);
      } else if (key != '') {
        // Better use Number.isInteger if the engine has EcmaScript 6
        if (key == '' || isNaN(key))  {
          displayActionFailure("Invalid key");
          return;
        }
        key = Number(key);
        deletePublication(key);
      }
    });

    $('#clear-store-button').click(function(evt) {
      clearObjectStore();
    });

    var search_button = $('#search-list-button');
    search_button.click(function(evt) {
      displayPubList();
    });

  }

  openDb();
  addEventListeners();

})(); // Immediately-Invoked Function Expression (IIFE)

Test the online live demo

Next step

If you want to start tinkering with the API, jump in to the reference documentation and check out the different methods.

See also

Reference

• IndexedDB API Reference
• Indexed Database API Specification
• Using IndexedDB in chrome

Tutorials

• A simple TODO list using HTML5 IndexedDB.
  Nota: This tutorial is based on an old version of the specification and does not work on up-to-date browsers - it still uses the removed setVersion() method.
• Databinding UI Elements with IndexedDB

Related articles

• IndexedDB — The Store in Your Browser

Firefox

• Mozilla interface files