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guideExtending the editor output

This guide focuses on customization of the one–way “downcast” pipeline of CKEditor 5. This pipeline transforms the data from the model to the editing view and the output data. The following examples do not customize the model and do not process the (input) data — you can picture them as post–processors (filters) applied to the output only.

If you want to learn how to load some extra content (element, attributes, classes) into the rich-text editor, check out the next guide of this section.

# Before starting

# Code architecture

It is recommended that the code that customizes the editor data and editing pipelines is delivered as plugins and all examples in this guide follow this convention.

Also for the sake of simplicity all examples use the same ClassicEditor, but keep in mind that code snippets will work with other editors, too.

Finally, none of the converters covered in this guide require to import any module from CKEditor 5 Framework, hence, you can write them without rebuilding the editor. In other words, such converters can easily be added to existing CKEditor 5 builds.

# Granular converters

You can create separate converters for the data and editing (downcast) pipelines. The former (dataDowncast) will customize the data in the editor output (e.g. when obtaining the editor data). The latter (editingDowncast) will only work for the content of the editor when editing.

If you do not want to complicate your conversion, you can just add a single (downcast) converter which will apply both to the data and the editing view. We did that in all examples to keep them simple but keep in mind you have options:

// Adds a conversion dispatcher for the editing downcast pipeline only.
editor.conversion.for( 'editingDowncast' ).add( dispatcher => {
    // ...
} );

// Adds a conversion dispatcher for the data downcast pipeline only.
editor.conversion.for( 'dataDowncast' ).add( dispatcher => {
    // ...
} );

// Adds a conversion dispatcher for both the data and the editing downcast pipelines.
editor.conversion.for( 'downcast' ).add( dispatcher => {
    // ...
} );

# CKEditor 5 inspector

CKEditor 5 inspector is an invaluable help when working with the model and view structures. It allows browsing their structure and checking selection positions like in typical browser developer tools. Make sure to enable the inspector when playing with CKEditor 5.

# Adding a CSS class to inline elements

In this example all links (<a href="...">...</a>) get the .my-green-link CSS class. This includes all links in the editor output (editor.getData()) and all links in the edited content (existing and future ones).

Note that the same behavior can be obtained with link decorators:

ClassicEditor
    .create( ..., {
        // ...
        link: {
            decorators: {
                addGreenLink: {
                    mode: 'automatic',
                    attributes: {
                        class: 'my-green-link'
                    }
                }
            }
        }
    } )

A custom CSS class is added to all links by a custom converter plugged into the downcast pipeline, following the default converters brought by the link feature:

// This plugin brings customization to the downcast pipeline of the editor.
function AddClassToAllLinks( editor ) {
    // Both the data and the editing pipelines are affected by this conversion.
    editor.conversion.for( 'downcast' ).add( dispatcher => {
        // Links are represented in the model as a "linkHref" attribute.
        // Use the "low" listener priority to apply the changes after the link feature.
        dispatcher.on( 'attribute:linkHref', ( evt, data, conversionApi ) => {
            const viewWriter = conversionApi.writer;
            const viewSelection = viewWriter.document.selection;

            // Adding a new CSS class is done by wrapping all link ranges and selection
            // in a new attribute element with a class.
            const viewElement = viewWriter.createAttributeElement( 'a', {
                    class: 'my-green-link'
                }, {
                    priority: 5
                } );

            if ( data.item.is( 'selection' ) ) {
                viewWriter.wrap( viewSelection.getFirstRange(), viewElement );
            } else {
                viewWriter.wrap( conversionApi.mapper.toViewRange( data.range ), viewElement );
            }
        }, { priority: 'low' } );
    } );
}

Activate the plugin in the editor:

ClassicEditor
    .create( ..., {
        extraPlugins: [ AddClassToAllLinks ],
    } )
    .then( editor => {
        // ...
    } )
    .catch( err => {
        console.error( err.stack );
    } );

Add some CSS styles for .my-green-link to see the customization in action:

.my-green-link {
    color: #209a25;
    border: 1px solid #209a25;
    border-radius: 2px;
    padding: 0 3px;
    box-shadow: 1px 1px 0 0 #209a25;
}

# Adding an HTML attribute to certain inline elements

In this example all links (<a href="...">...</a>) that do not have “ckeditor.com” in their href="..." get the target="_blank" attribute. This includes all links in the editor output (editor.getData()) and all links in the edited content (existing and future ones).

Note that similar behavior can be obtained with link decorators:

ClassicEditor
    .create( ..., {
        // ...
        link: {
            addTargetToExternalLinks: true
        }
    } )

The target attribute is added to all “external” links by a custom converter plugged into the downcast pipeline, following the default converters brought by the link feature:

// This plugin brings customization to the downcast pipeline of the editor.
function AddTargetToExternalLinks( editor ) {
    // Both the data and the editing pipelines are affected by this conversion.
    editor.conversion.for( 'downcast' ).add( dispatcher => {
        // Links are represented in the model as a "linkHref" attribute.
        // Use the "low" listener priority to apply the changes after the link feature.
        dispatcher.on( 'attribute:linkHref', ( evt, data, conversionApi ) => {
            const viewWriter = conversionApi.writer;
            const viewSelection = viewWriter.document.selection;

            // Adding a new CSS class is done by wrapping all link ranges and selection
            // in a new attribute element with the "target" attribute.
            const viewElement = viewWriter.createAttributeElement( 'a', {
                    target: '_blank'
                }, {
                    priority: 5
                } );

            if ( data.attributeNewValue.match( /ckeditor\.com/ ) ) {
                viewWriter.unwrap( conversionApi.mapper.toViewRange( data.range ), viewElement );
            } else {
                if ( data.item.is( 'selection' ) ) {
                    viewWriter.wrap( viewSelection.getFirstRange(), viewElement );
                } else {
                    viewWriter.wrap( conversionApi.mapper.toViewRange( data.range ), viewElement );
                }
            }
        }, { priority: 'low' } );
    } );
}

Activate the plugin in the editor:

ClassicEditor
    .create( ..., {
        extraPlugins: [ AddTargetToExternalLinks ],
    } )
    .then( editor => {
        // ...
    } )
    .catch( err => {
        console.error( err.stack );
    } );

Add some CSS styles for links with target="_blank" to mark them with with the “⧉” symbol:

a[target="_blank"]::after {
    content: '\29C9';
}

# Adding a CSS class to certain inline elements

In this example all links (<a href="...">...</a>) that do not have https:// in their href="..." attribute get the .unsafe-link CSS class. This includes all links in the editor output (editor.getData()) and all links in the edited content (existing and future ones).

Note that the same behavior can be obtained with link decorators:

ClassicEditor
    .create( ..., {
        // ...
        link: {
            decorators: {
                markUnsafeLink: {
                    mode: 'automatic',
                    callback: url => /^(http:)?\/\//.test( url ),
                    attributes: {
                        class: 'unsafe-link'
                    }
                }
            }
        }
    } )

The .unsafe-link CSS class is added to all “unsafe” links by a custom converter plugged into the downcast pipeline, following the default converters brought by the link feature:

// This plugin brings customization to the downcast pipeline of the editor.
function AddClassToUnsafeLinks( editor ) {
    // Both the data and the editing pipelines are affected by this conversion.
    editor.conversion.for( 'downcast' ).add( dispatcher => {
        // Links are represented in the model as a "linkHref" attribute.
        // Use the "low" listener priority to apply the changes after the link feature.
        dispatcher.on( 'attribute:linkHref', ( evt, data, conversionApi ) => {
            const viewWriter = conversionApi.writer;
            const viewSelection = viewWriter.document.selection;

            // Adding a new CSS class is done by wrapping all link ranges and selection
            // in a new attribute element with the "target" attribute.
            const viewElement = viewWriter.createAttributeElement( 'a', {
                    class: 'unsafe-link'
                }, {
                    priority: 5
                } );

            if ( data.attributeNewValue.match( /http:\/\// ) ) {
                if ( data.item.is( 'selection' ) ) {
                    viewWriter.wrap( viewSelection.getFirstRange(), viewElement );
                } else {
                    viewWriter.wrap( conversionApi.mapper.toViewRange( data.range ), viewElement );
                }
            } else {
                viewWriter.unwrap( conversionApi.mapper.toViewRange( data.range ), viewElement );
            }
        }, { priority: 'low' } );
    } );
}

Activate the plugin in the editor:

ClassicEditor
    .create( ..., {
        extraPlugins: [ AddClassToUnsafeLinks ],
    } )
    .then( editor => {
        // ...
    } )
    .catch( err => {
        console.error( err.stack );
    } );

Add some CSS styles for “unsafe” links to make them visible:

.unsafe-link {
    padding: 0 2px;
    outline: 2px dashed red;
    background: #ffff00;
}

# Adding a CSS class to block elements

In this example all second–level headings (<h2>...</h2>) get the .my-heading CSS class. This includes all heading elements in the editor output (editor.getData()) and in the edited content (existing and future ones).

Heading with .my-heading class

Regular heading

Some content.

A custom CSS class is added to all <h2>...</h2> elements by a custom converter plugged into the downcast pipeline, following the default converters brought by the headings feature:

The heading1 element in the model corresponds to <h2>...</h2> in the output HTML because in the default headings feature configuration <h1>...</h1> is reserved for the top–most heading of the webpage.

// This plugin brings customization to the downcast pipeline of the editor.
function AddClassToAllHeading1( editor ) {
    // Both the data and the editing pipelines are affected by this conversion.
    editor.conversion.for( 'downcast' ).add( dispatcher => {
        // Headings are represented in the model as a "heading1" element.
        // Use the "low" listener priority to apply the changes after the headings feature.
        dispatcher.on( 'insert:heading1', ( evt, data, conversionApi ) => {
            const viewWriter = conversionApi.writer;

            viewWriter.addClass( 'my-heading', conversionApi.mapper.toViewElement( data.item ) );
        }, { priority: 'low' } );
    } );
}

Activate the plugin in the editor:

ClassicEditor
    .create( ..., {
        extraPlugins: [ AddClassToAllHeading1 ],
    } )
    .then( editor => {
        // ...
    } )
    .catch( err => {
        console.error( err.stack );
    } );

Add some CSS styles for .my-heading to see the customization in action:

.my-heading {
    font-family: Georgia, Times, Times New Roman, serif;
    border-left: 6px solid #fd0000;
    padding-left: .8em;
    padding: .1em .8em;
}

# What’s next?

If you would like to read more about how to make CKEditor 5 accept more content, refer to the Preserving custom content guide.