Could not replicate

I can not replicate it either

I CAN replicate on Firefox and Safari.
Those that can't should test from last staging.

Exactly the same error pointed by @PhilETaylor

TypeError: (intermediate value).match is not a function[Learn More]
admin-article-readmore.min.js:1:161
window.insertReadmore
http://localhost:8888/newfolder/joomla40/media/com_content/js/admin-article-readmore.min.js:1:161
anonymous
http://localhost:8888/newfolder/joomla40/media/editors/tinymce/js/tinymce.min.js:3:1
setupEditor/</n.onclick
http://localhost:8888/newfolder/joomla40/media/editors/tinymce/js/tinymce.min.js:1:871
vm/r.fire
http://localhost:8888/newfolder/joomla40/media/vendor/tinymce/tinymce.min.js:1:187603
fire
http://localhost:8888/newfolder/joomla40/media/vendor/tinymce/themes/modern/theme.min.js:1:30800
a
http://localhost:8888/newfolder/joomla40/media/vendor/tinymce/themes/modern/theme.min.js:1:35026
u
http://localhost:8888/newfolder/joomla40/media/vendor/tinymce/tinymce.min.js:1:11719
C
http://localhost:8888/newfolder/joomla40/media/vendor/tinymce/tinymce.min.js:1:11870
l
http://localhost:8888/newfolder/joomla40/media/vendor/webcomponentsjs/js/webcomponents-hi-sd-ce.min.js:1:25807

Setting to confirmed

Here is the code for admin-article-readmore.es6.js:

(() => {
  'use strict';
  const options = window.Joomla.getOptions('xtd-readmore');

  window.insertReadmore = (editor) => {
    if (!options) {
      // Something went wrong!
      throw new Error(`XTD Button 'read more' not properly initialized`)
    }

    const content = window.Joomla.editors.instances[editor].getValue();

    if (content && !content.match(/<hr\s+id=("|')system-readmore("|')\s*\/*>/i)) {
      Joomla.editors.instances[editor].replaceSelection('<hr id="system-readmore">');
    } else {
      // TODO replace with joomla-alert
      alert(options.exists);
      return false;
    }
    return true;
  };
})();

If someone can make a pr I would really appreciate it ?

Thank @infograf768, now yes. I can replicate it. I thought I had the last staging.

@dgrammatiko
Looks like we have to modify
content.match to editor.match

Files concerned
/media/com_content/js/admin-article-readmore.es6.js
/media/com_content/js/admin-article-readmore.js

And then correct the minified files.

If I do that, no more errors.
Want me to do the PR?

NOTE: What we have in core is different from what you pasted above

Looks like we have to modify content.match to editor.match

Nope, I've already provided the code (it's also tested)

@dgrammatiko
I just wanted to help. The issue is NOT here in the e6 but in the admin-article-readmore.js and minified
Please do as you wish.

the admin-article-readmore.js is generated from the es6 file, that's the source

OK, then do it as I don't know how to.

BTW, with your proposal I guess you don't have an error but also you can insert as many read more (hr) as you like

@dgrammatiko
Looks like nobody made a PR with your code,
that works alright BTW.

I can do it but I need some details:
if I understand properly, the modified code should be applied to:
admin-article-readmore.es6.js
??
what I don't get is how to minify it. Can I use a minifying tool online ?
Or else ?

Yes in the es6 file. How to transpile to es5 and then minify can be found in #20396. You need npm installed.

I postponed until now my digging into npm. Guess this is the opportunity.
Tks for your tuto.

Thank your for stepping up to help.

closed see #21207