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Ext JS 4 Plugin and Extension Development

Chapter 1. Plugins and Extensions

This chapter introduces and defines the Ext JS plugins and extensions, the differences between them, and finally shows how to develop a plugin and an extension.

In this chapter we will cover:

What a plugin is
What an extension is
Differences between an extension and a plugin, and choosing the best option
Building an Ext JS plugin
Building an Ext JS extension

In this modern world of JavaScript, Ext JS is the best JavaScript framework that includes a vast collection of cross-browser utilities, UI widgets, charts, data object stores, and much more.

When developing an application, we mostly look for the best functionality support and components that offer it to the framework. But we usually face situations wherein the framework lacks the specific functionality or component that we need. Fortunately, Ext JS has a powerful class system that makes it easy to extend an existing functionality or component, or build new ones altogether.

Choosing the best option

When we need to enhance or change the functionality of an existing Ext JS component, we have several ways to do that, each of which has both advantages and disadvantages.

Let us assume we need to develop an SMS text field having a simple functionality of changing the text color to red whenever the text length exceeds the allocated length for a message; this way the user can see that they are typing more than one message. Now, this functionality can be implemented in three different ways in Ext JS, which is discussed in the following sections.

By configuring an existing class

We can choose to apply configuration to the existing classes. For example, we can create a text field by providing the required SMS functionality as a configuration within the listener's configuration, or we can provide event handlers after the text field is instantiated with the on method.

This is the easiest option when the same functionality is used only at a few places. But as soon as the functionality is repeated at several places or in several situations, code duplication may arise.

By creating a subclass or an extension

By creating an extension, we can easily solve the problem as discussed in the previous section. So, if we create an extension for the SMS text field by extending the Ext JS text field, we can use this extension at as many places as we need, and can also create other extensions by using this extension. So, the code is centralized for this extension, and changing one place can reflect in all the places where this extension is used.

But there is a problem: when the same functionality is needed for SMS in other subclasses of Ext JS text fields such as Ext JS text area field, we can't use the developed SMS text field extension to take advantage of the SMS functionality. Also, assume a situation where there are two subclasses of a base class, each of which provides their own facility, and we want to use both the features on a single class, then it is not possible in this implementation.

By creating a plugin

By creating a plugin, we can gain the maximum re-use of a code. As a plugin for one class, it is usable by the subclasses of that class, and also, we have the flexibility to use multiple plugins in a single component. This is the reason why if we create a plugin for the SMS functionality we can use the SMS plugin both in the text field and in the text area field. Also, we can use other plugins, including this SMS plugin, in the class.

Building an Ext JS plugin

Let us start developing an Ext JS plugin. In this section we will develop a simple SMS plugin, targeting the Ext JS textareafield component. The feature we wish to provide for the SMS functionality is that it should show the number of characters and the number of messages on the bottom of the containing field. Also, the color of the text of the message should change in order to notify the users whenever they exceed the allowed length for a message.

Here, in the following code, the SMS plugin class has been created within the Examples namespace of an Ext JS application:

Ext.define('Examples.plugin.Sms', {

  alias : 'plugin.sms',

  config : {

    perMessageLength : 160,
    defaultColor : '#000000',
    warningColor : '#ff0000'

  },

  constructor : function(cfg) {

    Ext.apply(this, cfg);

    this.callParent(arguments);
  },

  init : function(textField) {

    this.textField = textField;
    if (!textField.rendered) {
      textField.on('afterrender', this.handleAfterRender, this);
    }
    else {
      this.handleAfterRender();
    }
  },
  handleAfterRender : function() {

    this.textField.on({
      scope : this,
      change : this.handleChange
    });

    var dom = Ext.get(this.textField.bodyEl.dom);

    Ext.DomHelper.append(dom, {
      tag : 'div',
      cls : 'plugin-sms'
    });

  },

  handleChange : function(field, newValue) {

    if (newValue.length > this.getPerMessageLength()) {
      field.setFieldStyle('color:' + this.getWarningColor());
    }
    else {
      field.setFieldStyle('color:' + this.getDefaultColor());
    }
    this.updateMessageInfo(newValue.length);

  },

  updateMessageInfo : function(length) {

    var tpl = ['Characters: {length}<br/>', 'Messages:{messages}'].join('');
    var text = new Ext.XTemplate(tpl);
    var messages = parseInt(length / this.getPerMessageLength());

    if ((length / this.getPerMessageLength()) - messages > 0) {
      ++messages;
    }

    Ext.get(this.getInfoPanel()).update(text.apply({
      length : length,
      messages : messages
    }));

  },

  getInfoPanel : function() {

    return this.textField.el.select('.plugin-sms');

  }
});

Tip

Downloading the example code

You can download the example code files for all Packt books you have purchased from your account at http://www.packtpub.com. If you purchased this book elsewhere, you can visit http://www.packtpub.com/support and register to have the files e-mailed directly to you.

In the preceding plugin class, you can see that within this class we have defined a "must implemented" function called init. Within the init function, we check whether the component, on which this plugin is attached, has rendered or not, and then call the handleAfterRender function whenever the rendering is. Within this function, a code is provided, such that when the change event fires off the textareafield component, the handleChange function of this class should get executed; simultaneously, create an HTML <div> element within the handleAfterRender function, where we want to show the message information regarding the characters and message counter. And the handleChange function is the handler that calculates the message length in order to show the colored, warning text, and call the updateMessageInfo function to update the message information text for the characters length and the number of messages.

Now we can easily add the following plugin to the component:

{
    xtype : 'textareafield',
    plugins : ['sms']
}

Also, we can supply configuration options when we are inserting the plugin within the plugins configuration option to override the default values, as follows:

plugins : [Ext.create('Examples.plugin.Sms', {
  perMessageLength : 20,
  defaultColor : '#0000ff',
  warningColor : "#00ff00"
})]

Building an Ext JS extension

Let us start developing an Ext JS extension. In this section we will develop an SMS extension that exactly satisfies the same requirements as the earlier-developed SMS plugin.

We already know that an Ext JS extension is a derived class of existing Ext JS class, we are going to extend the Ext JS's textarea field that facilitates for typing multiline text and provides several event handling, rendering and other functionalities.

Here is the following code where we have created the Extension class under the SMS view within the Examples namespace of an Ext JS application:

Ext.define('Examples.view.sms.Extension', {
  extend : 'Ext.form.field.TextArea',
  alias : 'widget.sms',

  config : {

    perMessageLength : 160,
    defaultColor : '#000000',
    warningColor : '#ff0000'

  },

  constructor : function(cfg) {

    Ext.apply(this, cfg);

    this.callParent(arguments);
  },

  afterRender : function() {

    this.on({
      scope : this,
      change : this.handleChange
    });

    var dom = Ext.get(this.bodyEl.dom);

    Ext.DomHelper.append(dom, {
      tag : 'div',
      cls : 'extension-sms'
    });

  },

  handleChange : function(field, newValue) {

    if (newValue.length > this.getPerMessageLength()) {
      field.setFieldStyle('color:' + this.getWarningColor());
    }
    else {
      field.setFieldStyle('color:' + this.getDefaultColor());
    }
    this.updateMessageInfo(newValue.length);

  },

  updateMessageInfo : function(length) {

    var tpl = ['Characters: {length}<br/>', 'Messages:{messages}'].join('');
    var text = new Ext.XTemplate(tpl);
    var messages = parseInt(length / this.getPerMessageLength());

    if ((length / this.getPerMessageLength()) - messages > 0) {
      ++messages;
    }

    Ext.get(this.getInfoPanel()).update(text.apply({
      length : length,
      messages : messages
    }));

  },

  getInfoPanel : function() {

    return this.el.select('.extension-sms');

  }
});

As seen in the preceding code, the extend keyword is used as a class property to extend the Ext.form.field.TextArea class in order to create the extension class. Within the afterRender event handler, we provide a code so that when the change event fires off the textarea field, we can execute the handleChange function of this class and also create an Html <div> element within this afterRender event handler where we want to show the message information regarding the characters counter and message counter. And from this section, the logic to show the warning, message character counter, and message counter is the same as we used in the SMS plugin.

Now we can easily create an instance of this extension:

Ext.create('Examples.view.sms.Extension');

Also, we can supply configuration options when we are creating the instance of this class to override the default values:

Ext.create('Examples.view.sms.Extension', {
    perMessageLength : 20,
    defaultColor : '#0000ff',
    warningColor : "#00ff00"
});

The following is the screenshot where we've used the SMS plugin and extension:

In the above screenshot we have created an Ext JS window and incorporated the SMS extension and SMS plugin. As we have already discussed on the benefit of writing a plugin, we can not only use the SMS plugin with text area field, but we can also use it with text field.

Key benefits

Easy-to-follow examples on ExtJS plugins and extensions

Step-by-step instructions on developing ExtJS plugins and extensions

Provides a walkthrough of several useful ExtJS libraries and communities

Description

Ext JS is a pure JavaScript application framework for building interactive web applications using techniques such as Ajax, DHTML, and DOM scripting. Ext JS 4 Plugin and Extension Development is a practical, step-by-step tutorial which guides you to learn and develop ExtJS plugins and extensions. There are a lot of examples with explanations and plenty of code provided to make it easier and quicker to pick up. Starting with the fundamentals, this book introduces some of the ExtJS library and community provided plugins and extensions and finishes with several hands-on, real world development examples. You will get a clear concept of ExtJS plugins and extensions and learn how to use them. You will also learn how to develop an ExtJS plugin and extension by going through several examples with code and screenshots. Ext JS 4 Plugin and Extension Development book will provide you with the knowledge to develop ExtJS plugins and extensions using real-life examples.

What you will learn

Explore ExtJS plugins and extensions and the differences between them

Usage of ExtJS plugins and extensions

Follow along with code and screenshots to learn how to develop ExtJS plugins and extensions

Discover the ExtJS library and community provided extensions

Experience a step-by-step, hands-on development of several real-world ExtJS plugins and extensions

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Paperback book shipped to your preferred address

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Frequently bought together

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Ext JS 4 Plugin and Extension Development

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Total € 56.98

William Parker Oct 31, 2013

There have been several decent books covering Ext JS 4 published in the last year, some better than others, but unfortunately most follow the same pattern, this book is different."Ext JS 4 Plugin and Extension Development" makes a couple of assumptions about the reader's knowledge level and then jumps into the interesting stuff. I really like the way that the author lays the groundwork, explaining the pros and cons of Plugins and Extensions, and uses well known examples leading up to discussing how to go about developing your own.Why this works is that none of the examples are very complex, but they all have a real value, one or two are worth the price of the book given the value they will add to any 'modern' interface - the Intuitive Multiselect Combobox and Grid Search will both be in my next project.Most Ext JS books cover the subject in a similar manner and all fail in the same area, that being the server side code, so they ultimately force you to go and find another book for the server side, which probably has no reference to Ext JS - this book doesn't leave the reader looking for additional information, it covers everything they need to know - and its short...

Amazon Verified review

Ext JS 4 Plugin and Extension Development: This book makes it fast and fun for ExtJS developers to get to grips with developing plugins and extensions. The step-by-step instructions, with plentiful examples and code, will give you the skills in no time.

What do you get with Print?

Ext JS 4 Plugin and Extension Development

Chapter 1. Plugins and Extensions

What is a plugin?

What is an extension?

Differences between an extension and a plugin

Choosing the best option

By configuring an existing class

By creating a subclass or an extension

By creating a plugin

Building an Ext JS plugin

Tip

Building an Ext JS extension

Summary

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Ext JS 4 Plugin and Extension Development: This book makes it fast and fun for ExtJS developers to get to grips with developing plugins and extensions. The step-by-step instructions, with plentiful examples and code, will give you the skills in no time.

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