Help with adding custom option

I managed to add “Read More” option fo technews theme. So now if I toggle it ON it will show, and if it’s OFF it won’t show.

     {{#if @config.custom.feedReadMore}}
Read More
     {{/if}}

All works great, now I want to add when to show that “Read More” link. For example if text exceed 20 characters.
How can I compare that in template? What is condition for checking if string exceed X amount of characters?

This is the code for showing content from the post.

{{#if hasCustomExcerpt}}
   {{{ excerpt }}}
{{else}}
   <p>{{{ excerpt }}}</p>
{{/if}}