State of NLP in JavaScript World?

I am thinking of creating a web application. The app will analyze the English text. It will need to run text-readability algorithms such as https://en.wikipedia.org/wiki/Flesch%E2%80%93Kincaid_readability_tests.

The app will also need to find the syllable count of the words.

Are there reliable NLP JavaScript libraries (just like we've NLTK in Python) that you use in production?

Thanks in advance for all help.