JavaScript (abbreviated JS) is a single-threaded programming language that was created by Brendan Eich in 1995.
JavaScript is mainly used in web development to create games or make transitions. More than 1.5 billion websites utilize JS' features. That's about 95% of all websites! The language has become so popular that all major web browsers have dedicated engines to run it. But, not all browsers handle it the same.
JS and Python (multi-threaded programming language) can accomplish very similar tasks. However, GitHub (online repository) claims that JavaScript is used more widely.