A quite simple e-mail address obfuscation function using PHP and JS

emailobfuscator.php

<h2>Test</h2>
<?=obfuscateEmailWithJS("info@example.com",true)?><br>
<?=obfuscateEmailWithJS("doris.mustermann@example1.com",true,"Lorem ipsum")?><br>

<p>Lorem ipsum, dolor sit amet consectetur <?=obfuscateEmailWithJS("info@example.com",true)?> adipisicing elit. Cumque, veritatis? Cumque ut aut quidem suscipit saepe earum ducimus sunt nobis, cupiditate autem quaerat soluta atque veritatis similique minus sequi quasi?</p>





<?php

/**
 * obfuscateEmailWithJS
 *
 * @param string $email e-mail adress
 * @param bool $link output link or not
 * @param mixed $nojsText custom no-js placeholder text
 * @param string $prefix prefix of css class names and JS vars (may be changed to avoid conflicts)
 * @return void
 */
function obfuscateEmailWithJS(string $email, bool $link =false, $nojsText = false, $prefix="obf_"){
    // classname of anchor element
    $anchorname = $prefix.md5($email);
    if($link){
        $anchorname = $anchorname."_link";
    }

    // set default placeholder text, if none is given
    // NOTE: using email-like text in html comment **may** confuse spam bots 
    if(!$nojsText){
        $nojsText = "<!-- fakemail@example.com --> <!-- mailto:fakemail@example.com -->";
    }

    // split mail adress at "@" char
    $segments = explode('@',$email);

    // abort if splitting results in just one segment (no @ sign present in given $email)
    if(!count($segments) OR count($segments)==1){
        return;
    }

    // use ROT13 on segments, add quotes before and after
    $segments_rot = array();
    foreach ($segments as $key=>$value){
        $segments_rot[$key] = '"'.str_rot13($value).'"';
    }

    // prepare js array of ROT13 segments
    $js_array = '['.implode(',',$segments_rot).']';

    // output an empty HTML element as anchor for
    // js generated output in order to avoid document.write()
    // because document.write() should be avoided based on a 
    // warnin in google chrome
    $output = "<span class='{$prefix}anchor {$anchorname}'>{$nojsText}</span>";

    // javascript output
    // -- Source of rot13(): https://codereview.stackexchange.com/a/132140
    $output.= '<script>';

    $output.= 'function rot13(str) {
                var input     = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
                var output    = "NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm";
                var index     = x => input.indexOf(x);
                var translate = x => index(x) > -1 ? output[index(x)] : x;
                return str.split("").map(translate).join("");
            };

            var '.$prefix.'segments = '.$js_array.';
            var '.$prefix.'segments2 = [];
            var '.$prefix.'anchor = document.getElementsByClassName("'.$anchorname.'");
            '.$prefix.'segments.forEach(function(entry){
                '.$prefix.'segments2.push(rot13(entry));
            });';

    // to link or not to link
    if(!$link){
        $output.= 'for (let el of '.$prefix.'anchor) {
                    el.innerText = '.$prefix.'segments2.join("@");
                }';
    } else {
        $output.= 'for (let el of '.$prefix.'anchor) {
            el.innerHTML = "<a href=\'mailto:" + '.$prefix.'segments2.join("@") + "\'>" + '.$prefix.'segments2.join("@") + "</a>";
        }';
    }
            
            
    $output.= '</script>';


    return $output;

}


?>