JavaScript engines are essential programs that execute JavaScript code in web browsers and other environments, ensuring websites and applications function smoothly.

Some of the most popular JavaScript engines include V8, SpiderMonkey, JavaScriptCore (JSC), and Chakra.

1. V8, developed by Google, is known for its high performance and Just-In-Time (JIT) compilation and is used in Google Chrome, Microsoft Edge, Node.js, Deno, and other Chromium-based browsers.

1. Mozilla’s SpiderMonkey, one of the oldest JavaScript engines, powers Firefox and other Gecko-based browsers with its reliability and robust performance.

1. Apple’s JavaScriptCore (JSC), designed for Safari and WebKit-based browsers, focuses on speed and energy efficiency.

1. Microsoft’s Chakra engine, used in older versions of Microsoft Edge before its switch to Chromium, is recognized for its strong security and integration with Windows.

These engines significantly impact the speed and responsiveness of web pages, with their continuous evolution ensuring support for the latest JavaScript standards and delivering optimized performance.