'How can I add rel = "nofollow" to a link in CKEditor if it's an external link

i want to give rel="nofollow" to my external links which its content managed by ckeditor.

example.com = my site

externallink.com = any external link

For example:

<p>
    Lorem <a href="https://example.com/an-article.html">ipsum</a> dolar
    <a href="http://externallink.com/example.html" rel="nofollow">sit</a> amet.
</p>

This solution: 

editor.dataProcessor.htmlFilter.addRules(
{
    elements :
    {
        a : function( element )
        {
            if ( !element.attributes.rel )
                element.attributes.rel = 'nofollow';
        }
    }
});

from https://stackoverflow.com/a/6930940/1848929 adds nofollow to all a elements.

How can i filter only external links?

Also deep doc about CKEditor Data Processor: http://docs.cksource.com/CKEditor_3.x/Developers_Guide/Data_Processor

Note: Stackoverflow's text editor using these question's answer. Check two links' rel attribute in this question.

I'm using <script src="//cdn.ckeditor.com/4.5.10/standard/ckeditor.js"></script> from cdn on my pages.

javascriptjqueryhtmlckeditornofollow


Solution 1:[1]

I solved it like;

CKEDITOR.on('instanceReady', function(ev) {
        var editor = ev.editor;
        editor.dataProcessor.htmlFilter.addRules({
                elements : {
                    a : function( element ) {
                        if ( !element.attributes.rel ){
                           //gets content's a href values
                            var url = element.attributes.href;
                           //extract host names from URLs 
                            var hostname = (new URL(url)).hostname;
                            if ( hostname !== window.location.host && hostname !=="youranothersite.com") {
                                element.attributes.rel = 'nofollow';
                            }
                        }
                    }
                }
            });
    })

Solution 2:[2]

This solution also works in Internet Explorer:

CKEDITOR.on('instanceReady', function(ev) {
    var editor = ev.editor;
    editor.dataProcessor.htmlFilter.addRules({
        elements : {
            a : function( element ) {
                if ( !element.attributes.rel ){
                    //gets content's a href values
                    var url = element.attributes.href;

                    //extract host names from URLs (IE safe)
                    var parser = document.createElement('a');
                    parser.href = url;

                    var hostname = parser.hostname;
                    if ( hostname !== window.location.host) {
                        element.attributes.rel = 'nofollow';
                        element.attributes.target = '_blank';
                    }
                }
            }
        }
    });
})

Solution 3:[3]

So you need to compare hosts, something like this should work. 

a : function( element )
    {
        if ( element.host !== window.location.host ) {
            element.attributes.rel = 'nofollow';
        }
    }

Solution 4:[4]

Be shure to check hostname for empty value and for relative paths for do not add target='_blank' and rel='nofollow' for links like "tel:+70000000000" or "mailto:[email protected]"

CKEDITOR.on('instanceReady', function (ev) {
    var editor = ev.editor;
    editor.dataProcessor.htmlFilter.addRules({
        elements: {
            a: function (element) {
                var url = element.attributes.href;
                var parser = document.createElement('a');
                parser.href = url;
                var hostname = parser.hostname;
                if (hostname && hostname !== "localhost" && hostname !== window.location.host) { // ???? ??????? ??????
                    if (!element.attributes.target)
                        element.attributes.target = '_blank';
                    if (!element.attributes.rel)
                        element.attributes.rel = 'nofollow';
                }
            }
        }
    });
});

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1 hakkikonu
Solution 2 Tom-Steve Watzke
Solution 3 epascarello
Solution 4

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