Lista de muitos sites onde você pode praticar e exercitar o javascript (principalmente para resolver problemas da vida real ou praticar deliberadamente)
Inglês
https://www.theodinproject.com/
https://rosettacode.org/wiki/Rosetta_Code
https://projecteuler.net/
https://www.freecodecamp.org/news/the-10-most-popular-coding-challenge-websites-of-2016-fb8a5672d22f/
https://www.freecodecamp.org/learn/
https://app.codility.com/programmers/lessons
https://www.w3resource.com/javascript-exercises/
https://www.codingame.com
https://www.learn-js.org
https://javascript.info
https://www.hackerrank.com
https://www.codecademy.com/catalog/language/javascript
https://www.codewars.com/?language=javascript
http://reactivex.io/learnrx/
https://github.com/raloliver/matematica-para-programadores
https://www.w3schools.com/js/js_exercises.asp
https://edabit.com/challenges/javascript
https://practity.com/582-2/
https://www.frontendmentor.io/challenges
https://github.com/florinpop17/app-ideas
https://ydkjs-exercises.com
Português
https://www.devchallenge.com.br/
https://nerdin.com.br/testes
https://br.spoj.com/
https://www.algomania.com.br/questions/
https://github.com/estevanmaito/apenas-crie-websites
https://dojopuzzles.com/
https://professor.leonardomeirelles.com/wp/lista-de-exercicios-javascript
https://7daysofcode.io/
Caso algum link pare de funcionar ou tenha mais sugestões, por favor, deixe um comentário.