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## Terms, Icons, and Labels

Many classes have shortcut names used when creating (instantiating) a class with a configuration object. The shortcut name is referred to as an `alias` (or `xtype` if the class extends Ext.Component). The alias/xtype is listed next to the class name of applicable classes for quick reference.

### Access Levels

Framework classes or their members may be specified as `private` or `protected`. Else, the class / member is `public`. `Public`, `protected`, and `private` are access descriptors used to convey how and when the class or class member should be used.

- Public classes and class members are available for use by any other class or application code and may be relied upon as a stable and persistent within major product versions. Public classes and members may safely be extended via a subclass.

- Protected class members are stable `public` members intended to be used by the owning class or its subclasses. Protected members may safely be extended via a subclass.

- Private classes and class members are used internally by the framework and are not intended to be used by application developers. Private classes and members may change or be omitted from the framework at any time without notice and should not be relied upon in application logic.

### Member Types

- Config - The configuration options for a class.
- Property - Set once a class is instantiated. *See Read Only below.
- Method - Actions that can be performed by a class. Methods should be read as instance methods and can only be called from a instance of a given class. Static methods that can be called directly from the class itself will have a `static` label next to the method name. *See Static below.
- Event - Events are specific to the framework event system allowing for classes to programmatically raise an event to be handled by one or more event handler methods. DOM events, while handled by the framework event system, are not specifically described within the API documentation. *For DOM events refer to the event reference page from MDN.
- Theme Variable - Variables used by the visual theme engine employed by the framework.
- Theme Mixin - Functions used by the visual theme engine employed by the framework and may use values set in various Theme Variables.

### Member Syntax

Below is an example class member that we can disect to show the syntax of a class member (the lookupComponent method as viewed from the Ext.button.Button class in this case).

Ext.container.Container
view source
lookupComponent ( item ) : Ext.Component
protected

Called when a raw config object is added to this container either during initialization of the items config, or when new items are added), or {@link #insert inserted.

This method converts the passed object into an instanced child component.

This may be overridden in subclasses when special processing needs to be applied to child creation.

Parameters

item : Object

The config object being added.

Returns
Ext.Component

The component to be added.

Let's look at each part of the member row:

- Expand/Collapse - On the left-hand size of the member row is a control used to expand and collapse each member row to show / hide member details.
- Member Name - The name of the class member (`lookupComponent` in this example)
- Method Param - Any required or optional params used by a method (or passed to an event handler method) will be listed next to the method name within parenthesis (`( item )` in this example)
- Return type - The class instance or javascript object returned by the method or property (`Ext.Component` in this case). This may be omitted for methods that do not return anything other than `undefined` or may display as multiple possible values separated by a forward slash `/` signifying that what is returned may depend on the results of the method call (i.e. a method may return a Component if a get method calls is successful or `false` if unsuccessful which would be displayed as `Ext.Component/Boolean`).
- Flags - Any flags applicable to the member will be displayed next (`PROTECTED` in this example - see the Flags section below)
- Member Origin - On the right-hand side of the member row is the class where the member was initially described (`Ext.container.Container` in this example). The source class will be displayed as a blue link if the member originates from the current class and gray if it is inherited from an ancestor or mixed-in class.
- Member Source - On the right-hand side below the member origin class is a link to view the member's source (`view source` in the example)
- Params List - Each param for a class method will be listed using the same name found above in parenthesis, the type of class or object expected, and a description of the param (`item : Object` in the example).
- Returns - If a class returns a value other than `undefined` a "Returns" section will note the type of class or object returned and a description (`Ext.Component` in the example)
- Since (not shown in the example) - Some members will show which version of the product the member was first introduced (i.e. `Available since 3.4.0` - not pictured in the example) just after the member description
- Default (not shown in the example) - Configs often show the default config value to be applied to a class instance if not overridden (i.e. `Defaults to: false`)

### Member Flags

The API documentation uses a number of flags to further commnicate the class member's function and intent. The label may be represented by a text label, an abbreviation, or an icon.

- Required - Required config when instantiating a class
- Bindable - The config has a setter which allows this config to be set via ViewModel binding
- Read Only - The property may be read, but cannot be used to configure / re-configure a class instance at runtime
- Singleton - Singleton classes are instantiated immediately once defined and may not be instantiated manually
- Static - A static method or property is a method or property belonging to the class itself, not an instance of the class
- Chainable - Refers to methods that return the class instance back when called.
  This enables chained method calls like: `classInstance.method1().method2().etc();`
- Deprecated - A class or member that is scheduled for removal in a future framework version and is provided in the current version for backwards compatibility.
  Deprecated classes and members will have a message directing you to the preferred class / method going forward.
- Removed - A removed class or member that exists in documentation only as a reference for users upgrading between framework versions
- Template - A method defined within a base class designed to be overridden by subclasses
- Abstract - A class or member may be be defined as abstract. Abstract classes and members establish a class structure and provide limited, if any, code. Class-specific code will be furnished via overrides in subclasses.
- Preventable - Events marked preventable will not fire if `false` is returned from an event handler

### Class Icons

- Indicates a framework class

- A singleton framework class. *See the singleton flag for more information

- A component-type framework class (any class within the Ext JS framework that extends Ext.Component)

- Indicates that the class, member, or guide is new in the currently viewed version

### Member Icons

- Indicates a class member of type `config`

- Indicates a class member of type `property`

- Indicates a class member of type `method`

- Indicates a class member of type `event`

- Indicates a class member of type `theme variable`

- Indicates a class member of type `theme mixin`

- Indicates that the class, member, or guide is new in the currently viewed version

## Navigation and Features

### Class Member Quick-Nav Menu

Just below the class name on an API doc page is a row of buttons corresponding to the types of members owned by the current class. Each button shows a count of members by type (this count is updated as filters are applied). Clicking the button will navigate you to that member section. Hovering over the member-type button will reveal a popup menu of all members of that type for quick navigation.

### Getter and Setter Methods

Getting and setter methods that correlate to a class config option will show up in the methods section as well as in the configs section of both the API doc and the member-type menus just beneath the config they work with. The getter and setter method documentation will be found in the config row for easy reference.

### History Bar

Your page history is kept in localstorage and displayed (using the available real estate) just below the top title bar. By default, the only search results shown are the pages matching the product / version you're currently viewing. You can expand what is displayed by clicking on the button on the right-hand side of the history bar and choosing the "All" radio option. This will show all recent pages in the history bar for all products / versions.

Within the history config menu you will also see a listing of your recent page visits. The results are filtered by the "Current Product / Version" and "All" radio options. Clicking on the button will clear the history bar as well as the history kept in local storage.

If "All" is selected in the history config menu the checkbox option for "Show product details in the history bar" will be enabled. When checked, the product/version for each historic page will show alongside the page name in the history bar. Hovering the cursor over the page names in the history bar will also show the product/version as a tooltip.

### Search and Filters

Both API docs and guides can be searched for using the search field at the top of the page.

On API doc pages there is also a filter input field that filters the member rows using the filter string. In addition to filtering by string you can filter the class members by access level and inheritance. This is done using the checkboxes at the top of the page. Note that filtering out `private` members also filters the API class navigation tree.

Clicking on an empty search field will show your last 10 searches for quick navigation.

### API Doc Class Metadata

Each API doc page (with the exception of Javascript primitives pages) has a menu view of metadata relating to that class. This metadata view will have one or more of the following:

- Alternate Name - One or more additional class name synonymns (in Ext JS 6.0.0 the `Ext.button.Button` class has an alternate class name of `Ext.Button`). Alternate class names are commonly maintained for backward compatibility.
- Hierarchy - The hierararchy view lists the inheritance chain of the current class up through its ancestor classes up to the root base class.
- Mixins - A list of classes that are mixed into the current class
- Inherited Mixins - A list of classes that are mixed into an ancestor of the current class
- Requires - All classes required to be defined for the class to be instantiated
- Uses - A list of classes potentially used by the class at some point in its lifecycle, but not necessarily requried for the class to initially be instantiated
- Subclasses - Classes that extend the current class

### Expanding and Collapsing Examples and Class Members

Runnable examples (Fiddles) are expanded on a page by default. You can collapse and expand example code blocks individually using the arrow on the top-left of the code block. You can also toggle the collapse state of all examples using the toggle button on the top-right of the page. The toggle-all state will be remembered between page loads.

Class members are collapsed on a page by default. You can expand and collapse members using the arrow icon on the left of the member row or globally using the expand / collapse all toggle button top-right.

### Desktop -vs- Mobile View

Viewing the docs on narrower screens or browsers will result in a view optimized for a smaller form factor. The primary differences between the desktop and "mobile" view are:

- Global navigation will be located in a menu on the left-hand side accessible via the hamburger menu icon. The menu houses the following (on most pages):
  - The name of the current product (as a link to the product landing page)
  - The Sencha icon used to navigate back to the documentation home page
  - The product menu drop-down button
  - Tabs of navigation trees for the API docs and guides
- Current context navigation and tools is located on the right-hand side accessible via the gear icon. The context menu houses teh following:
  - The global search input field
  - (API doc) A "Filters" tab with the member filter, expand / collapse all examples button, expand / collapse all member rows button, the access level filter checkboxes, and the counts of each member
  - (API doc) A "Related Classes" tab containing the menu of metadata related to the current class
  - (Guides) The table of contents for the guide

### Viewing the Class Source

The class source can be viewed by clicking on the class name at the top of an API doc page. The source for class members can be viewed by clicking on the "view source" link on the right-hand side of the member row.

Basics of OOP
Classic Toolkit

##
Ext JS 6.2.0 - Modern Toolkit

Guides
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top

# Basic OOP / Class-Based Programming Concepts

JavaScript is a classless, prototype-oriented language and one of its most powerful features is flexibility. That said, Class-based programming is arguably the most popular model of Object Oriented Programming (OOP). This style generally emphasizes strong-typing, encapsulation, and standard coding conventions.

JavaScript’s flexibility comes with the cost of being unpredictable. Without a unified structure, JavaScript code can be difficult to understand, maintain, and re-use. On the other hand, class-based code is more likely to be predictable, extensible, and scalable over time.

Fortunately, Ext JS’ class system provides you with the best of both worlds. You gain a flexible, extensible, and scalable implementation of class-based programming with JavaScript's flexibility.

This guide is intended for any developer that wants to learn or review Ext JS' concept of OOP and class-based programming. We will cover the following topics:

- Classes and Instances

- Inheritance (polymorphism)

- Encapsulation

## Classes and Instances

It is important to be able to clearly distinguish between classes and instances. In simple terms, a class is the blueprint of a concept, while an instance is the actualization of the blueprint. Let's look at some examples:

- "Building" is a class, while the Empire State Building is an instance of "Building".

- "Dog" is a class, while Lassie is an instance of "Dog".

- "Computer" is a class, while the computer you’re using is an instance of "Computer".

A class defines the base structure, properties, and behavior of its instances. For example, using the same classes described above:

- All instances of "Building" have a given number of floors (structure), an address, and opening hours (properties). Also, assuming these are "smart buildings", they can close and lock their main entrance as needed (behavior).

- All instances of "Dog" have 4 legs and a tail (structure). They also have a name (property) and are able to bark (behavior).

- All instances of "Computer" have a CPU and some form of memory (structure), a model name (property), and are able to be turned on and off (behavior).

Let's define a class that will serve as our base for exploring concepts of class-based programming. We'll start with the "Square" class, which represents a square along with a simple method for calculating its area.

You can define the Square class with the following syntax:

Sample Code

     // Define a new class named: 'Square'
     Ext.define('Square', {
         // The side property represents the length of the side
         // It has a default value of 0
         side: 0,

         // It also has a method to calculate its area
         getArea: function() {
             // We access the 'side' property to calculate area
             return this.side * this.side;
         }
     });

     // We use Ext.create to create an instance of our Square class
     var sq = Ext.create('Square');

     // The value of the 'side' property
     // This is not the best way to do this, which we'll discuss below
     sq.side = 4;

     // Display a message and show the result of this calculation
     Ext.Msg.alert('Message', 'The area is: ' + sq.getArea());

This is a bare-bones implementation of a class using Ext JS. While it does meet our goals of representing a square and providing a method to calculate its area, it is not ideal or good practice.

### Constructors

Let’s improve this example by utilizing a constructor. A constructor is a special function that gets called when a Class is instantiated. First, let's change the way we set the value of Square's side. By utilizing the constructor, we can remove the ‘ugly’ line from the example above.

Sample Code

     Ext.define('Square', {
         side: 0,

         // This is a special function that gets called
         // when the object is instantiated
         constructor: function (side) {
             // It receives the side as a parameter
             // If defined, it is set as the square's side value
             if (side) {
                 this.side = side;
             }
         },

         getArea: function () {
             return this.side * this.side;
         }
     });

     // Thanks to the constructor, we can pass 'side's' value
     // as an argument of Ext.create
     // This is a slightly more elegant approach.
     var sq = Ext.create('Square', 4);

     // The passed value is assigned to the square's side property
     // Display a message to make sure everything is working
     Ext.Msg.alert('Message', 'The area is: ' + sq.getArea());

If you want to pass two or more property values to the constructor, you can do it using an object literal as follows:

Sample Code

     Ext.define('Square', {
         side: 0,
         // We have added two more configs
         color: 'red',
         border: true,

         // Pass a config object, which contains 'side's' value
         constructor: function(config) {
             // Once again, this is not yet the best syntax
             // We'll get to that in the next example
             if (config.side) {
                 this.side = config.side;
             }
             if (config.color) {
                 this.color = config.color;
             }
             // border is a boolean so we can skip the if block
             this.border = config.border;
         },

         getArea: function() {
             return this.side * this.side;
         }
     });

     // We pass an object containing properties/values
     var sq = Ext.create('Square', {
         side: 4,
         border: false
     });

     // Now display a message that uses the other two properties
     // Note that we're accessing them directly (i.e.: sq.color)
     // This will change in the next section
     Ext.Msg.alert('Message',
          ['The area of the',sq.color,'square',
          (sq.border?'with a border':''),'is:',
          sq.getArea()].join(' ')
     );

### Apply

We can clean up the constructor further using `Ext.apply`. Ext.apply copies all the properties of config to the specified object.

Note: The constructor will change again in the inheritance section.

Sample Code

     Ext.define('Square', {
         side: 0,
         color: 'red',
         border: true,

         constructor: function(config) {
             // Use Ext.apply to not set each property manually
             // We'll change this again in the "Inheritance" section
             Ext.apply(this,config);
         },

         getArea: function() {
             return this.side * this.side;
         }
     });

     var sq = Ext.create('Square', {
         side: 4,
         border: false
     });

     Ext.Msg.alert('Message',
          ['The area of the',sq.color,'square',
          (sq.border?'with a border':''),'is:',
          sq.getArea()].join(' ')
     );

### Defining more classes

Let's add Circle and Rectangle classes in order to show a few slight deviations from the Square example.

Sample Code

     Ext.define('Square', {
         side: 0,
         color: 'red',
         border: true,

         constructor: function(config) {
             Ext.apply(this, config);
         },

         getArea: function() {
             return this.side * this.side;
         }
     });

     Ext.define('Rectangle', {
         //Instead of side, a rectangle cares about base and height
         base: 0,
         height: 0,
         color: 'green',
         border: true,

         constructor: function(config) {
             Ext.apply(this, config);
         },

         getArea: function() {
             // The formula is different
             return this.base * this.height;
         }
     });

     Ext.define('Circle', {
         // A circle has no sides, but radius
         radius: 0,
         color: 'blue',
         border: true,

         constructor: function(config) {
             Ext.apply(this, config);
         },

         getArea: function() {
             // Just for this example, fix the precision of PI to 2
             return Math.PI.toFixed(2) * Math.pow(this.radius, 2);
         }
     });

     var square = Ext.create('Square', {
                 side: 4,
                 border: false
             }),
         rectangle = Ext.create('Rectangle', {
                 base: 4,
                 height: 3
             }),
         circle = Ext.create('Circle', {
                 radius: 3
             });

     // This message will now show a line for each object
     Ext.Msg.alert('Message', [
         ['The area of the', square.color, 'square',
          (square.border ? 'with a border' : ''), 'is:',
          square.getArea()].join(' '),

         ['The area of the', rectangle.color, 'rectangle',
         (rectangle.border ? 'with a border' : ''), 'is:',
         rectangle.getArea()].join(' '),

         ['The area of the', circle.color, 'circle',
         (circle.border ? 'with a border' : ''), 'is:',
         circle.getArea()].join(' ')
     ].join('<br />'));

## Inheritance

Before diving into the concept of inheritance, let's review the following example. As you can see below, we’ve added an additional method to the Square class and changed the way the test message is generated:

Sample Code

     Ext.define('Square', {
         side: 0,
         color: 'red',
         border: true,

         constructor: function(config) {
             Ext.apply(this, config);
         },

         getArea: function() {
             return this.side * this.side;
         },

         // This function will return the name of this shape
         getShapeName: function () {
             return 'square';
         }
     });

     //This function generates a sentence to display in the test dialog
     function generateTestSentence(shape) {
         return ['The area of the', shape.color, shape.getShapeName(),
                 (shape.border ? 'with a border' : ''),
                 'is:', shape.getArea()].join(' ');
     }

     var square = Ext.create('Square', {
         side: 4,
         border: false
     });

     Ext.Msg.alert('Message', generateTestSentence(square));

In the next example, we'll apply the same changes to the Rectangle and Circle classes:

Sample Code

     Ext.define('Square', {
         side: 0,
         color: 'red',
         border: true,

         constructor: function(config) {
             Ext.apply(this, config);
         },

         getArea: function() {
             return this.side * this.side;
         },

         getShapeName: function () {
             return 'square';
         }
     });

     Ext.define('Rectangle', {
         base: 0,
         height: 0,
         color: 'green',
         border: true,

         constructor: function(config) {
             Ext.apply(this, config);
         },

         getArea: function() {
             return this.base * this.height;
         },

         getShapeName: function () {
             return 'rectangle';
         }
     });

     Ext.define('Circle', {
         radius: 0,
         color: 'blue',
         border: true,

         constructor: function(config) {
             Ext.apply(this, config);
         },

         getArea: function() {
             return Math.PI.toFixed(2) * Math.pow(this.radius, 2);
         },

         getShapeName: function () {
             return 'circle';
         }
     });

     // Generates a sentence that will be displayed in the test dialog
     function generateTestSentence(shape) {
         return ['The area of the', shape.color, shape.getShapeName(),
         (shape.border ? 'with a border' : ''), 'is:',
         shape.getArea()].join(' ');
     }

     var square = Ext.create('Square', {
                 side: 4,
                 border: false
             }),
         rectangle = Ext.create('Rectangle', {
                 base: 4,
                 height: 3
             }),
         circle = Ext.create('Circle', {
                 radius: 3
             });

     Ext.Msg.alert('Message', [
         generateTestSentence(square),
         generateTestSentence(rectangle),
         generateTestSentence(circle)
     ].join('<br />'));

If you carefully review the above example, you may notice a lot of repetition. This can make your code difficult to maintain and prone to errors. The concept of inheritance helps us consolidate repetitive code and makes it easier to understand and maintain.

### Parent and child classes

By applying the concept of inheritance, we can simplify and reduce the repetitive code by giving child classes properties of a parent class:

Sample Code

     // The shape class contains common code to each shape class
     // This allows the passing of properties on child classes
     Ext.define('Shape', {
         // Let's define common properties here and set default values
         color: 'gray',
         border: true,

         // Let's add a shapeName property and a method to return it
         // This replaces unique getShapeName methods on each class
         shapeName: 'shape',

         constructor: function (config) {
             Ext.apply(this, config);
         },

         getShapeName: function () {
             return this.shapeName;
         }
     });

     Ext.define('Square', {
         // Square extends from Shape so it gains properties
         // defined on itself and its parent class
         extend: 'Shape',

         // These properties will 'override' parent class properties
         side: 0,
         color: 'red',
         shapeName: 'square',

         getArea: function() {
             return this.side * this.side;
         }
     });

     //This function generates a sentence to display in the test dialog
     function generateTestSentence(shape) {
         return ['The area of the', shape.color, shape.getShapeName(),
                 (shape.border ? 'with a border' : ''),
                 'is:', shape.getArea()].join(' ');
     }

     var square = Ext.create('Square', {
         side: 4
     });

     // Since Square extends from Shape, this example will work since
     // all other properties are still defined, but now by 'Shape'
     Ext.Msg.alert('Message',
          [ generateTestSentence(square) ].join('<br />'));

We can even move the `generateTestSentence()` method to the Shape class:

Sample Code

     Ext.define('Shape', {
         color: 'gray',
         border: true,
         shapeName: 'shape',

         constructor: function (config) {
             Ext.apply(this, config);
         },

         getShapeName: function () {
             return this.shapeName;
         },

         // This function will generate the test sentence for this shape,
         // so no need to pass it as an argument
         getTestSentence: function () {
             return ['The area of the', this.color, this.getShapeName(),
                     (this.border ? 'with a border' : ''),
                     'is:', this.getArea()].join(' ');
         }
     });

     Ext.define('Square', {
         extend: 'Shape',

         side: 0,
         color: 'red',
         shapeName: 'square',

         getArea: function() {
             return this.side * this.side;
         }
     });

     var square = Ext.create('Square', {
         side: 4
     });

     // The generateTestSentence function doesn't exist anymore
     // so use the one that comes with the shape
     Ext.Msg.alert('Message',
                   [ square.getTestSentence() ].join('<br />'));

As you can see, the properties on the child class will override properties on the parent class if they're both set. For instance, the Shape's `shapeName` is "shape". However, since `shapeName` is set on the Square class as well, it overrides the parent class's value. If the child class doesn't have a property set, it will inherit said property from the parent.

## Encapsulation

In the previous examples, you may notice we’re accessing instance properties by calling them directly. For instance, getting square's color by accessing "square.color". You can set the value directly as well:

Sample Code

     Ext.define('Shape', {
         color: 'gray',
         border: true,
         shapeName: 'shape',

         constructor: function (config) {
             Ext.apply(this, config);
         },

         getShapeName: function () {
             return this.shapeName;
         },

         getTestSentence: function () {
             return ['The area of the', this.color, this.getShapeName(),
                     (this.border ? 'with a border' : ''),
                     'is:', this.getArea()].join(' ');
         }
     });

     Ext.define('Square', {
         extend: 'Shape',

         side: 0,
         color: 'red',
         shapeName: 'square',

         getArea: function() {
             return this.side * this.side;
         }
     });

     var square = Ext.create('Square', {
         side: 4
     });

     // Set the value of 'side' to 5 instead of the initial 4
     // While not bad, this is something that should be avoided
     square.side = 5;

     // Set the value of 'side' to a string instead of a number
     // String is not a valid value. This is an example of why
     // direct access to the properties should be avoided.
     // Open access is prone to error.
     square.side = 'five';

     // The area will be reported as NaN
     Ext.Msg.alert('Message',
                   [ square.getTestSentence() ].join('<br />'));

## Config Block

To prevent direct read/write of an object's properties, we’ll make use of Ext JS’ `config` block. This will automatically restrict access to the object's properties so they can only be set and retrieved using accessor methods.

Accessor methods are automatically generated getters and setters for anything in a class's config block. For instance, if you have `shapeName` in a config block, you get `setShapeName()` and `getShapeName()` by default.

Note: The config block should only include new configs unique to its class. You should not include configs already defined in a parent class's config block.

Sample Code

     Ext.define('Shape', {
         // All properties inside the config block have
         // their accessor methods automatically generated
         config: {
             color: 'gray',     // creates getColor|setColor
             border: true,      // creates getBorder|setBorder
             shapeName: 'shape' // creates getShapeName|setShapeName
         },

         constructor: function (config) {
             Ext.apply(this, config);
             // Initialize the config block for this class
             // This auto-generates the accessor methods
             // More information on this in the next section
             this.initConfig(config);
         },

         // We have removed the getShapeName method
         // It's auto-generated since shapeName is in the config block

         // Now we can use the accessor methods instead
         // of accessing the properties directly
         getTestSentence: function () {
             return ['The area of the', this.getColor(),
                     this.getShapeName(),
                     (this.getBorder() ? 'with a border' : ''), 'is:',
                     this.getArea()].join(' ');
         }
     });

     Ext.define('Square', {
         extend: 'Shape',

         // In a child class, the config block should only
         // contain new configs particular for this class
         config: {
             side: 0 //  getSide and setSide are now available
         },

         // Parent class properties are defined outside the config block
         color: 'red',
         shapeName: 'square',

         getArea: function() {
             // We're using the accessor methods of the 'side' config
             return this.getSide() * this.getSide();
         }
     });

     var square = Ext.create('Square', {
         side: 4
     });

     // The following line won't modify the value of 'side' anymore
     square.side = 'five';

     // To modify it instead, we'll use the setSide method:
     square.setSide(5);

     // The area will be reported as 25
     Ext.Msg.alert('Message',
                    [ square.getTestSentence() ].join('<br />'));

## Ext.Base class

In Ext JS, all classes are children of a common base class unless explicitly specified. This base class is `Ext.Base`.

Just like our Square class extends from Shape, Shape automatically extends from Ext.Base.
Based on this logic, the following code:

Sample Code

     Ext.define('Shape', {
         // Properties and methods here
     });

is actually equivalent to this:

Sample Code

     Ext.define('Shape', {
         extend: 'Ext.Base'
         // Properties and methods here
     });

This is why we can use this.initConfig(config); in the constructor of Shape. `initConfig()` is a method of Ext.Base and is inherited by anything extending from it. `initConfig()` initializes the config block for its class and auto-generates the accessor methods.

### Real property encapsulation

The main goal of encapsulation is to protect objects from unwanted and/or invalid property modification. These modifications would inevitably result in errors.

For example, when using the `config` block to avoid direct property modification, nothing is currently preventing invalid values from being passed to the accessor methods. That is, nothing prevents us from calling square.setSide('five'), which would result in an error since side expects a numeral.

Let’s prevent this by using the apply method. Apply is a template method which allows you to test the proposed value before modification. This method copies all of the properties of config to the specified object.

Since 'side' is a property defined through the 'config' block, we can make use of this template method to act before the value is actually modified, such as checking if the new value for 'side' is indeed a number.

Sample Code

     Ext.define('Shape', {
         config: {
             color: 'gray',
             border: true,
             shapeName: 'shape'
         },

         constructor: function (config) {
             Ext.apply(this, config);
             this.initConfig(config);
         },

         getTestSentence: function () {
             return ['The area of the', this.getColor(),
                     this.getShapeName(),
                     (this.getBorder() ? 'with a border' : ''),
                     'is:', this.getArea()].join(' ');
         }
     });

     Ext.define('Square', {
         extend: 'Shape',
         config: {
             side: 0
         },

         color: 'red',
         shapeName: 'square',

         getArea: function() {
             return this.getSide() * this.getSide();
         },

         // 'side' is a property defined through the 'config' block,
         // We can use this method before the value is modified
         // For instance, checking that 'side' is a number
         applySide: function (newValue, oldValue) {
             return (Ext.isNumber(newValue)? newValue : oldValue);
         }
     });

     var square = Ext.create('Square', {
         side: 4
     });

     // The following line won't modify the value of 'side'
     square.setSide('five');

     // The area will be reported as 16
     Ext.Msg.alert('Message',
                   [ square.getTestSentence() ].join('<br />'));

## Conclusion

We hope that this guide clarifies the basic concepts of OOP and Class-based programming in Ext JS. Be sure to check out the Class System guide for additional information on how to leverage Ext JS’ class system when making your own applications. As always, if you have questions regarding guide content, be sure to ask on the community forums or by submitting a Support ticket through the Support Portal (Sencha Support customer access only).

## Ext JS 6.2.0 - Modern Toolkit

## Ext JS

### 6.x

6.2.0 EA (classic) (modern)
6.0.2 (classic) (modern)
6.0.1 (classic) (modern)
6.0.0 (classic) (modern)

### 5.x

5.1.3 5.1.2 5.1.1 5.1.0 5.0.1 5.0.0

### 4.x

4.2.5 4.1.3 4.0.7

### 3.x

3.4.0

## Sencha Test

Sencha Test

## Cmd

Cmd

## GXT

4.x 3.x

## IDE Plugins

IDE Plugins

## Sencha Inspector

Sencha Inspector

## Architect

Architect 3 Architect 4 EA

## Touch

### 2.x

Touch 2.4 Touch 2.3 Touch 2.2 Touch 2.0

## Web Application Manager

Web Application Manager
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