Your comments
Textastic 7 uses the syntax definition of Sublime Text 3 to highlight C++ source code.
If you send me a sample code file, I can open it in Textastic and send you a screenshot of how it is highlighted if that would help you.
Great to hear that it works now!
It works great for me on iOS 11.4.1 with Textastic 7.0.3 on my iPhone X. Here is a screenshot.

I don't know why the select button doesn't appear for you, sorry.
It works for me: I put the file into Local Files/#Textastic/tcm/. Then I quit Textastic using the multi-tasking switcher and restarted it. I could then open a file, go to the File Properties and select "TCM-notes" as the syntax definition.
However I would need to have an example file to see if the syntax definition works as intended.
I would have to try to reproduce this on my own device. Do you know if there is something like a public demo server that I can use for this?
The second and third folder structure should work. Can you please send me the file so I can try to reproduce it on my device?
The JavaScript code must be either inside a script tag in a .html file or if you want to have it in a separate .js file, you need to reference that file from a .html file. Then you need to show the preview of that .html file to make the console.log statement work.
So for example this would work:
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>Console Test</title>
<script>
console.log('this is a test');
</script>
</head>
<body>
</body>
</html>
Textastic 7 now has built-in TypeScript syntax highlighting.
Ok, I'm glad it works now for you.
Customer support service by UserEcho
Können Sie mir bitte ein Beispiel zeigen mit der Info, was genau nicht erkannt wird?