Hello,
Please take a look at the Modern Javascript Tutorial, it was recently translated to Japanese at https://ja.javascript.info ;).
The tutorial is free and open-source, has theory and tasks with tests to practice.
As the author of the original English version, I'm not speaking Japanese.
Right now, the site is totally unknown to Japanese public, that's why I post here. Please tell me, how's the quality of the translation?
If you consider this a valuable resource, please help to spread the word about it.