Creating a Simple CKEditor Plugin (Part 2)

The aim of this tutorial is to demonstrate how to extend an existing CKEditor plugin with context menu support as well as the possibility to edit a previously inserted element.

Instead of creating a new plugin, this time we are going to expand on the functionality of the Abbreviation plugin created in the previous installment of the tutorial series.

We need to start where we previously left off. You can download the whole plugin folder including the icon and the fully commented source code.

If you have any doubt about the contents of the plugin and its configuration, refer to the Creating a Simple CKEditor Plugin (Part 1) tutorial.

Please note that since CKEditor 4.1 most of the plugins integrate the Advanced Content Filter for correct behaviour and compliance.
You need to set the configuration option config.allowedContent = true that disables the feature or integrate filtering to follow this guide. For more information, please refer to the official Advanced Content Filter integration guide.

Context Menu Support

Context menu support in CKEditor is implemented by the Context Menu plugin.

The context menu implementation should be placed inside the init function in the plugin file, following the command and button definitions:

if ( editor.contextMenu ) {
    editor.addMenuGroup( 'abbrGroup' );
    editor.addMenuItem( 'abbrItem', {
        label: 'Edit Abbreviation',
        icon: this.path + 'icons/abbr.png',
        command: 'abbrDialog',
        group: 'abbrGroup'
    });
}

The if check here is a "best practice". If for some reason the Context Menu plugin will be removed or not available, the menu registration should not take place (otherwise an exception is thrown).

Then, considering that we want the context menu option for the Abbreviation plugin to be separated from standard context menu items, we used the editor.addMenuGroup function to register a new menu group called abbrGroup.

Using the addMenuItem function we can now register a new menu item that will belong to the newly created group. The label and icon properties let us set the context menu item name and its icon, respectively. To make the context menu item open the Abbreviation Properties dialog window, we need to set the command property to use the abbrDialog command.

Showing the Menu Option "In Context"

However, when we reload the CKEditor instance and add an abbreviation, the context menu does not contain the newly created Edit Abbreviation item. We now need to enable the Abbreviation context menu for each selected <abbr> element:

if ( editor.contextMenu ) {
    ... the previous menu creation code ...

    editor.contextMenu.addListener( function( element ) {
        if ( element.getAscendant( 'abbr', true ) ) {
            return { abbrItem: CKEDITOR.TRISTATE_OFF };
        }
    });
}

By using the addListener function we will add an event listener function that will be called whenever the context menu is fired.

At this point we just check if the current element, or any of its parents, is a <abbr>. If true, we simply return the menu item to activate - abbrItem - saying that it is enable but not in "selected state" (CKEDITOR.TRISTATE_OFF).

The Edit Abbreviation item is now visible in the context menu of an <abbr> element. Once selected, it opens the Abbreviation Properties dialog window due to the use of the abbrDialog command.

The context menu works — but only partially. It opens the Abbreviation Properties dialog window for the abbreviation, but the editing feature does not really work. The Abbreviation and Explanation fields are empty:

If you try to enter some values into these fields and accept the changes, a new <abbr> element will be added on the position of the cursor in the document.

It is time to work on the selection logic so that editing an inserted element would not create a new one, but use the previously entered values.

Dialog Window Logic

The editing behavior for a previously inserted element will use the onShow function that is defined for the plugin dialog window and is executed when the dialog window is opened. This function will be defined above the onOk function that we will also need to refactor later.

onShow: function() {
    // The code that will be executed when a dialog window is loaded.
}

Getting the Selected Element

We will need to start with the selection logic.

To get to the element that is selected by the user (either highlighted or keyboard or just having the caret inside), we need to use the editor.getSelection function:

var selection = editor.getSelection();

We will also use the selection.getStartElement to get the element in which the selection starts, and assign it to the element variable:

var element = selection.getStartElement();

Insert and Edit Modes

Still our dialog must work both to add and to edit <abbr> elements. Because of this, we introduce some startup that identifies the proper case:

if ( element )
    element = element.getAscendant( 'abbr', true );

if ( !element || element.getName() != 'abbr' ) {
    element = editor.document.createElement( 'abbr' );
    this.insertMode = true;
}
else
    this.insertMode = false;

We just used similar code that we used in context menu checks, to figure out if the selected element, or any ancestor, is a <abbr>.

To differentiate between adding a new element and editing an existing one, we will create a new insertMode flag. It will be set to true in the "add new element" scenario. If an <abbr> element already exists, the insertMode flag will be set to false.

We will now store a reference to the <abbr> element in the element variable since we will need to access it in the new version of the onOK function later.

this.element = element;

Setup Functions

The onShow function will finish with a call to the setupContent function that will invoke the setup functions for the element. Each parameter that will be passed on to the setupContent function will also be passed on to the setup functions.

if ( !this.insertMode )
    this.setupContent( element );

For the above code to work we will however first need to define the setup functions themselves. In order to do that, we will revisit the code of the dialog window UI elements.

The setup function for the Abbreviation text field needs to get the contents of the <abbr> element by using the getText function in order to populate the field with its value by using the setValue function.

A similar approach can be used for the Explanation field, although in this case we will need to get the contents of the title attribute of the <abbr> element by using the getAttribute function in order to populate the field with its value by using the setValue function again.

elements: [
    {
        type: 'text',
        id: 'abbr',
        label: 'Abbreviation',
        validate: CKEDITOR.dialog.validate.notEmpty( "Abbreviation cannot be empty" ),
        setup: function( element ) {
            this.setValue( element.getText() );
        }
    },
    {
        type: 'text',
        id: 'title',
        label: 'Explanation',
        validate: CKEDITOR.dialog.validate.notEmpty( "Title cannot be empty" ),
        setup: function( element ) {
            this.setValue( element.getAttribute( "title" ) );
        }
    }
]

Since the Advanced Settings tab contains a single Id text field that reflects the contents of the id attribute, we will use the same combination of the getAttribute and setValue function as in case of the Explanation text field.

elements: [
    {
        type: 'text',
        id: 'id',
        label: 'Id',
        setup: function( element ) {
            this.setValue( element.getAttribute( "id" ) );
        }
    }
]

When you reload the page, add an abbreviation, and then attempt to modify it by opening the context menu and selecting Edit Abbreviation, the Abbreviation Properties dialog window will now re-open with the Abbreviation and Explanation fields already filled in with the contents of the edited element.

Suppose you were to change the abbreviation spelling into lower case. Replace the contents of the text fields as follows and click the OK button.

This operation fails! The modified values do not replace the contents of the first abbreviation, but are used to create a new abbreviation element inserted inside the first one, at the position of the cursor.

Why is that so? It is because the current edition of the onOk function does not differentiate between adding an element and modifying it, so it simply inserts the values supplied in the dialog window fields into the <abbr> that it creates and adds this element to the document.

Commit Functions

To correct this error, we will need to re-write the code of the onOk function to account for both scenarios. The function can now, in fact, be stripped to the minimum.

Firstly, we will define the variables for the dialog window (dialog) and the <abbr> element (abbr).

The insertMode flag created in the onShow function can then be used to switch between the creation of a new element and modification of the existing one. If we are in the insert mode, we add a new <abbr> element to the document. We then use the commitContent function to populate the element with values entered by the user. Every parameter that is passed to the commitContent function will also be passed on to the commit functions themselves.

onOk: function() {
    var dialog = this,
        abbr = dialog.element;

    dialog.commitContent( abbr );

    if ( dialog.insertMode )
        editor.insertElement( abbr );
}

To make the commitContent method work we will however first need to define the commit functions themselves. In order to do that, we will have to revise the code of the dialog window UI elements again.

The commit function for the Abbreviation text field needs to get the value entered by the user by using the getValue function in order to set the contents of the <abbr> element by using the setText function.

A similar approach can be used for the retrieval of the Explanation field contents, although in this case we will need to set the contents of the title attribute of the <abbr> element by using the setAttribute function.

elements: [
    {
        type: 'text',
        id: 'abbr',
        label: 'Abbreviation',
        validate: CKEDITOR.dialog.validate.notEmpty( "Abbreviation cannot be empty" ),
        setup: function( element ) {
            this.setValue( element.getText() );
        },
        commit: function( element ) {
            element.setText( this.getValue() );
        }
    },
    {
        type: 'text',
        id: 'title',
        label: 'Explanation',
        validate: CKEDITOR.dialog.validate.notEmpty( "Title cannot be empty" ),
        setup: function( element ) {
            this.setValue( element.getAttribute( "title" ) );
        },
        commit: function( element ) {
            element.setAttribute( "title", this.getValue() );
        }
    }
]

Similarly, since the Advanced Settings tab contains an Id text field that reflects the contents of the id attribute, we will use the same combination of the getValue and setAttribute function as in case of the Explanation text field. This time, however, we will also need to account for the possibility of removing the attribute value by the user during the modification of the element. If we are not in the insert mode (which means we are editing an existing element) and the Id field is empty, we will use the removeAttribute method to delete the id element of an existing abbreviation.

elements: [
    {
        type: 'text',
        id: 'id',
        label: 'Id',
        setup: function( element ) {
            this.setValue( element.getAttribute( "id" ) );
        },
        commit: function ( element ) {
            var id = this.getValue();
            if ( id )
                element.setAttribute( 'id', id );
            else if ( !this.insertMode )
                element.removeAttribute( 'id' );
        }
    }
]

Full Source Code

The full contents of the plugin.js file are as follows:

CKEDITOR.plugins.add( 'abbr', {
    init: function( editor ) {
        var iconPath = this.path + 'images/icon.png';

        editor.addCommand( 'abbrDialog',new CKEDITOR.dialogCommand( 'abbrDialog' ) );

        editor.ui.addButton( 'Abbr', {
            label: 'Insert Abbreviation',
            command: 'abbrDialog',
            icon: iconPath
        });

        if ( editor.contextMenu ) {
            editor.addMenuGroup( 'abbrGroup' );
            editor.addMenuItem( 'abbrItem', {
                label: 'Edit Abbreviation',
                icon: this.path + 'icons/abbr.png',
                command: 'abbr',
                group: 'abbrGroup'
            });

            editor.contextMenu.addListener( function( element ) {
                if ( element.getAscendant( 'abbr', true ) ) {
                    return { abbrItem: CKEDITOR.TRISTATE_OFF };
                }
            });
        }
    }
});

CKEDITOR.dialog.add( 'abbrDialog', function( editor ) {
            return {
                title: 'Abbreviation Properties',
                minWidth: 400,
                minHeight: 200,
                contents: [
                    {
                        id: 'tab1',
                        label: 'Basic Settings',
                        elements: [
                            {
                                type: 'text',
                                id: 'abbr',
                                label: 'Abbreviation',
                                validate: CKEDITOR.dialog.validate.notEmpty( "Abbreviation field cannot be empty" ),
                                setup: function( element ) {
                                    this.setValue( element.getText() );
                                },
                                commit: function( element ) {
                                    element.setText( this.getValue() );
                                }
                            },
                            {
                                type: 'text',
                                id: 'title',
                                label: 'Explanation',
                                validate: CKEDITOR.dialog.validate.notEmpty( "Explanation field cannot be empty" ),
                                setup: function( element ) {
                                    this.setValue( element.getAttribute( "title" ) );
                                },
                                commit: function( element ) {
                                    element.setAttribute( "title", this.getValue() );
                                }
                            }
                        ]
                    },
                    {
                        id: 'tab2',
                        label: 'Advanced Settings',
                        elements: [
                            {
                                type: 'text',
                                id: 'id',
                                label: 'Id',
                                setup: function( element ) {
                                    this.setValue( element.getAttribute( "id" ) );
                                },
                                commit: function ( element ) {
                                    var id = this.getValue();
                                    if ( id )
                                        element.setAttribute( 'id', id );
                                    else if ( !this.insertMode )
                                        element.removeAttribute( 'id' );
                                }
                            }
                        ]
                    }
                ],

                onShow: function() {
                    var selection = editor.getSelection(),
                        element = selection.getStartElement();
                    if ( element )
                        element = element.getAscendant( 'abbr', true );

                    if ( !element || element.getName() != 'abbr' || element.data( 'cke-realelement' ) ) {
                        element = editor.document.createElement( 'abbr' );
                        this.insertMode = true;
                    }
                    else
                        this.insertMode = false;

                    this.element = element;

                    if ( !this.insertMode )
                        this.setupContent( this.element );
                },

                onOk: function() {
                    var dialog = this,
                        abbr = this.element;

                    this.commitContent( abbr );

                    if ( this.insertMode )
                        editor.insertElement( abbr );
                }
            };
        });

You can also download the whole plugin folder inluding the icon and the fully commented source code.

Working Example

The code of the extended Abbreviation plugin is now ready. When you click the Insert Abbreviation toolbar button, the Abbreviation Properties dialog window will open. Fill in the obligatory Abbreviation and Explanation fields and click the OK button.

The newly added abbreviation will be inserted into the document and will be displayed using the default styling of your browser. In Firefox, for example, the abbreviation will be underlined using a dotted line and the explanation will be displayed in a tooltip.

If you want to edit the abbreviation, select it and open its context menu. Choose the Edit Abbreviation option to open the dialog window again, filled in with the contents of the element. Modify the abbreviation and click OK.

Voilà! The abbreviation was updated and its contents replaced with texts entered in the dialog window.