Error while loading 0x800a1391 - JavaScript runtime error: tinymce is undefined

Hi makumbisulaiman58,

You can simple use the CDN directly instead of using local file.

Using CDN directly will automatically gets changes if updated or new feature is added to it.

Refer below:

<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/tinymce/4.0.20/tinymce.min.js"></script>
<script type="text/javascript">
    tinymce.init({ selector: 'textarea', width: 300 });
</script>

Glad to assist!