How JavaScript Engines Turn Source Code Into Executable Instructions

JavaScript was created in 1995 by Brendan Eich at Netscape in just 10 days, originally to add interactivity to static web pages. Today it powers not only browsers but also servers via Node.js, mobile apps through React Native, and desktop software like VS Code. Every JavaScript environment relies on a dedicated engine — Chrome and Node.js use V8, Firefox uses SpiderMonkey, and Safari uses JavaScriptCore — to interpret and run code. These engines process JavaScript through parsing, interpreting, and compiling steps collectively known as Just-In-Time (JIT) compilation. When a program runs, the engine creates an execution context, a self-contained environment holding the variables, functions, and scope needed to evaluate the code.