Engine (1/3)
Explain the internals of JavaScript engines, including concepts like the Call Stack, Heap, Event Loop, and Just-In-Time (JIT) compilation.
    JavaScript engines are responsible for interpreting and executing JS code in browsers and other environments. They consist of several key components that work together to process and run JavaScript code efficiently.
    • Call Stack: The Call Stack is a fundamental data structure that keeps track of function calls and their execution contexts. It follows the Last-In-First-Out (LIFO) principle, meaning the most recently called function is executed first and removed from the stack when completed.
    • Heap: The Heap is a memory region where objects, closures, and variables are allocated. It's the place where dynamic memory allocation occurs during the execution of a program. Objects created in the code are stored in the Heap, and their memory is managed by the garbage collector.
    • Event Loop: The Event Loop is a core concept in JavaScript engines, especially in environments like web browsers. It manages asynchronous operations and ensures that non-blocking code execution is possible.
    • Callbacks and Promises: Asynchronous code, such as callbacks and Promises, is placed in the Event Queue when their execution context is ready to be processed.
    • Event Loop Phases: The Event Loop has multiple phases, including checking timers, executing I/O operations, and handling callbacks. These phases ensure that asynchronous code is executed in the correct order.
    • Just-In-Time (JIT) Compilation: JIT compilation is a technique used by modern JavaScript engines to optimise code execution. It involves translating JavaScript code into machine code at runtime, improving performance compared to traditional interpretation.
    Steps of JIT Compilation:
    • Parsing: The engine parses the JavaScript code and creates an Abstract Syntax Tree (AST).
    • Compilation: The AST is converted into intermediate bytecode representation.
    • Optimization: The engine applies various optimization techniques to the bytecode, such as inlining, dead code elimination, and function inlining.
    • Execution: The optimized bytecode is executed by the engine's runtime.
    • Memory Management and Garbage Collection: JavaScript engines manage memory allocation and deallocation to prevent memory leaks. The Garbage Collector identifies objects that are no longer referenced and frees up memory occupied by these objects.
    • V8 Engine: The V8 engine is used in modern web browsers like Google Chrome. It's known for its efficient JIT compilation and optimization techniques.
    • SpiderMonkey Engine: Mozilla's SpiderMonkey engine is used in Firefox. It also supports JIT compilation and employs a generational garbage collector.
    • JavaScriptCore, also known as Nitro, is used in Apple's Safari browser. It supports both JIT compilation and Ahead-of-Time (AOT) compilation.
    • Microsoft's Chakra engine was used in older versions of Internet Explorer and Microsoft Edge. It also supports JIT compilation and optimization.
    JIT in different engines:
    • V8 Engine: The V8 engine is used in modern web browsers like Google Chrome. It's known for its efficient JIT compilation and optimization techniques.
    • SpiderMonkey Engine: Mozilla's SpiderMonkey engine is used in Firefox. It also supports JIT compilation and employs a generational garbage collector.
    • JavaScriptCore, also known as Nitro, is used in Apple's Safari browser. It supports both JIT compilation and Ahead-of-Time (AOT) compilation.
    • Microsoft's Chakra engine was used in older versions of Internet Explorer and Microsoft Edge. It also supports JIT compilation and optimization.

    In summary, JavaScript engines comprise several key components like the Call Stack, Heap, Event Loop, JIT Compilation, and Memory Management. These components work together to interpret, optimize, and execute JavaScript code efficiently while handling asynchronous operations and managing memory resources.