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

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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"
})]