How to calculate the length of text with special characters?

There is nothing built in JavaScript to help you distinguish these label combinations from other characters. You could build something of course using the reference information from http://unicode.org . :-)

... but at least one person seems to have already done this for you: https://github.com/orling/grapheme-splitter

Enter the grapheme-splitter.js library. It can be used to properly split JavaScript strings into what the user-user might call individual letters (or "extended grapheme clusters" in Unicode terminology), regardless of their internal representation. It is an implementation of the UAX-29 Unicode standard.

const words = 'a̋b̋';
const splitter = new GraphemeSplitter();
const graphemes = splitter.splitGraphemes(words);
console.log(graphemes);

      

        
        
        
      

    

This results in two entries in graphemes

, "a̋"

and "b̋"

. (Can't follow live example, direct links to original github pages are prohibited.)