Wednesday, October 26, 2011

HTML5: A complete overview

The last two days I have been giving a presentation about the capabilities of HTML5. For all the people who weren’t able to follow these sessions, I have put my slides on Slideshare.

I noticed that it is hard to find out what all the functionalities are of HTML5, that is why I made a little overview. It’s possible it will be out dated soon, but this is because HTML5 is a dynamic standard that still keeps growing and the major browser are still bringing up proposals for new features. Enjoy the slides…

Tuesday, October 25, 2011

Indexed DB: Defining the database structure

In previous post I have been talking about the basic concepts in the Indexed DB and how you can open/create a database and a database connection. Today I will tell you how you can construct your own database structure. This includes defining the object store where we can store our objects and defining indexes. These indexes will be used when searching into the objects we store in our database.

version_change transaction

There exists only one way to define your object stores and indexes, and this is in a VERSION_CHANGE transaction. We can start this transaction by calling the setVersion method on the database connection. When a database is initially created, the version of the database is an empty string. By passing a string as version to the setVersion method, we add object stores and indexes. This we do by defining the onsuccess event. We can also provide error handeling trough the onerror event.

var dbreq = dbConnection.setVersion(version);
dbreq.onsuccess = function (event) {
      // Here we put code to create object stores or indexes

dbreq.onerror = function (event) {
      // Here we put code to handle an error while changing the version

dbreq.onabort = function (event) {
      // Here we put code to handle an abort when changing the database version

If we are using the IE 9 Indexed DB prototype, we need to commit the transaction. In all other browsers this is not necessary because the implementation of Indexed DB determines that every transaction is committed by default when closed. If a transaction should be aborted you have to do this explicitly.

dbreq.onsuccess = function (event) {
       var txn;
       if (event.result) {
             txn = event.result;
       // Here we put code to create object stores or indexes
       if(typeof(txn.commit) != "undefined")

Because a database can’t have multiple versions at one time, the only way you can change the version is by closing all other connections to the database. This also means no new connections can’t be opened until the VERSION_CHANGE transaction is completed. A blocked event will be raised when a connection to the database is still open when changing the version.

dbreq.onblocked = function (event) {
// Here we put code to handle an abort when changing the database version

Creating an objectStore

Once we started the VERSION_CHANGE transaction, we can start adding or deleting object stores. We can do this by calling the createObjectStore method. As first parameter we need to pass the name of the object store. Optionally you can can add two extra parameters. The first one is JSON object with two fields. The first field is a keyPath, when this is provided, the key of the object store will be determined by the field that has the name given in the string of the key path. The second field determines if the object store should have a key generator.

The last parameter we pass is the same as the autoIncrement field in the second parameter. We do this to enable the object store to have a key generator in the IE9 prototype. When using Firefox, Chrome and IE 10, you don’t need to pass this parameter.

The following combinations of a KeyPath and autoIncrement are possible:

Key path Auto increment Description
Empty False This object store can hold any kind of value, even primitive values like numbers and strings. You must supply a separate key argument whenever you want to add a new value to the object store.
Provided False This object store can only hold JavaScript objects. The objects must have a property with the same name as the key path.
Empty True This object store can hold any kind of value. The key is generated for you automatically, or you can supply a separate key argument if you want to use a specific key.
Provided True This object store can only hold JavaScript objects. Usually a key is generated and the value of the generated key is stored in the object in a property with the same name as the key path. However, if such a property already exists, the value of that property is used as key rather than generating a new key.

                                              , { "keyPath": "keyPath"
                                                , "autoIncrement": true }
                                              , true);

removing an object store

When we want to remove an object store, the only thing we need to pass is the name of the object store we want to remove.


Creating an INDEX

Once we created our object store, we can add indexes to it. These indexes are object stores as well, but the key of these key/value pairs is the key path of the index. This means that in this object store that multiple keys with the same value are allowed. When we want to create an index we need to provide a name and a key path for them. Optionally we can provide a JSON object with a unique and multiplerow field.

Field Description Support
unique A boolean value indicating whether the index allows duplicate values. If this attribute is "true", duplicate values are not allowed. Duplicate values are allowed when this attribute is "false" (the default value). This means when you add an object to an object store where an index with a unique value on "true". You will get an exception when you add an object with a duplicate value in the field of the key path of the index. IE 10
multiplerow A boolean value that describes determines the results when multiple rows in the object store match individual key values. When this happens, the resulting object is an array. If this parameter is "true", the resulting array contains a single item; the key of the item contains an array of the matching values. When this parameter is "false" (the default), the result array contains one item for each item that matches the key value. IE 10

                         , "keyPath"
                         , { unique: false });

If we want to create an index in IE 9 Indexed DB prototype, we need to pass the boolean value for the uniqueness as parameter and not as a JSON object.

, "keyPath"
, false);

Deleting an index

The last action we can do in the VERSION_CHANGE event is deleting an existing index. We can do this by passing the name of the index we want to delete.


Sunday, October 2, 2011

Indexed DB: Creating, opening and deleting a database

In my last post I provided some more information about the structure of the Indexed DB database. Today, I will dive into code and tell you how to create, open and delete a database. There are some small differences between the browsers, but I will handle that at the specific parts of code.

The code I will show will be the Asynchronous implementation of the API. In my previous post I have said no browser does implement the synchronous API, but I was wrong. The IE 10 Preview 3 also implements the Synchronous implementation, but you should only use it in combination with web workers, because it freezes the UI if you don’t.

Initializing the Indexed DB API

First things first: the Indexed DB API is still in draft, so this means the unified Indexed DB property on the window element isn’t implemented yet. Every browser uses his on prefix to use the API, but we can assign this to the Indexed DB property. This gives us a way to us the Indexed DB on the same way.

Initializing the Firefox implementation

if (window.mozIndexedDB) {
            window.indexedDB = window.mozIndexedDB;
            window.IDBKeyRange = window.IDBKeyRange;
            window.IDBTransaction = window.IDBTransaction;

Initializing the Chrome implementation

if (window.webkitIndexedDB) {
            window.indexedDB = window.webkitIndexedDB;
            window.IDBKeyRange = window.webkitIDBKeyRange;
            window.IDBTransaction = window.webkitIDBTransaction;

Initializing the IE 10 Preview 3 implementation (You’ll need to be running the Windows 8 Developer Preview to run this)

if (window.msIndexedDB) {
            window.indexedDB = window.msIndexedDB;

Initializing the IE prototype implementation

if (navigator.appName == 'Microsoft Internet Explorer') {
            window.indexedDB = new ActiveXObject("SQLCE.Factory.4.0");
            window.indexedDBSync = new ActiveXObject("SQLCE.FactorySync.4.0");

            if (window.JSON) {
                window.indexedDB.json = window.JSON;
                window.indexedDBSync.json = window.JSON;
            } else {
                var jsonObject = {
                    parse: function (txt) {
                        if (txt === "[]") return [];
                        if (txt === "{}") return {};
                        throw { message: "Unrecognized JSON to parse: " + txt };
                window.indexedDB.json = jsonObject;
                window.indexedDBSync.json = jsonObject;


            // Add some interface-level constants and methods.
            window.IDBDatabaseException = {
                UNKNOWN_ERR: 0,
                NON_TRANSIENT_ERR: 1,
                NOT_FOUND_ERR: 2,
                CONSTRAINT_ERR: 3,
                DATA_ERR: 4,
                NOT_ALLOWED_ERR: 5,
                SERIAL_ERR: 11,
                RECOVERABLE_ERR: 21,
                TRANSIENT_ERR: 31,
                TIMEOUT_ERR: 32,
                DEADLOCK_ERR: 33

            window.IDBKeyRange = {
                SINGLE: 0,
                LEFT_OPEN: 1,
                RIGHT_OPEN: 2,
                LEFT_BOUND: 4,
                RIGHT_BOUND: 8

            window.IDBRequest = {
                INITIAL: 0,
                LOADING: 1,
                DONE: 2

            window.IDBTransaction = {
                READ_ONLY: 0,
                READ_WRITE: 1,
                VERSION_CHANGE: 2

            window.IDBKeyRange.only = function (value) {
                return window.indexedDB.range.only(value);

            window.IDBKeyRange.leftBound = function (bound, open) {
                return window.indexedDB.range.leftBound(bound, open);

            window.IDBKeyRange.rightBound = function (bound, open) {
                return window.indexedDB.range.rightBound(bound, open);

            window.IDBKeyRange.bound = function (left, right, openLeft, openRight) {
                return window.indexedDB.range.bound(left, right, openLeft, openRight);

Creating and opening a database

Once we have our Indexed DB initialized, we can start the real thing. Creating a database. There is no specific method to create a new database, but when we call the open method, a database will be created if it doesn’t exists. After that a connection to the database will be opened. To open or create a database, the only thing you need is a name.

var dbreq =“database name”);

dbreq.onsuccess = function (event) {
        var dbConnection;
        // IE prototype Implementation
        if (event.result) {
                dbConnection = event.result;
        //IE 10 Preview 3, Firefox & Chrome implementation
        else {
                dbConnection = dbreq.result;

dbreq.onerror = function (event) {
       // Log or show the error message

Calling the open method, will return an IDBRequest object. On this object we can attach an onerror function and an onsuccess function. The onerror event will provide handling the error returned by the open function, here you can provide logging or error handling. In the onsuccess event, the database connection will be opened. We can now start using the database connection.

As you can see in code, IE prototype implementation is handling this on an other way then IE 10 Preview 3, Firefox and Chrome. In the IE prototype implementation we get the result (the database connection) out the parameter that is passed trough with the onsuccess function. For IE 10 Preview 3, Firefox and Chrome, we get the result from the IDBRequest object. This is the implementation that was defined by the W3C.

Deleting a database

Deleting the database will happen almost the same way as opening a database. You provide the name of the database you want to delete, and the database will get deleted. The error event will only be called when something goes wrong. Providing a database name that doesn’t exists, will not result in an error and the onsuccess function will get called.

var dbreq = window.indexedDB.deleteDatabase(“database name”);
        dbreq.onsuccess = function (event) {
             // Database deleted
        dbreq.onerror = function (event) {
            // Log or show the error message

Now we can create, open and delete a database. In one of my next posts, I will show you how you can create/change your database structure.