The V8 engine is a high-performance JavaScript engine developed by Google and used in Google Chrome, Node.js, and other environments. It is designed to increase the performance of JavaScript execution by compiling JavaScript code directly into machine code that a computer's processor can execute. Here's a detailed explanation of how the V8 engine works:
Just-In-Time (JIT) Compilation
V8 employs Just-In-Time (JIT) compilation to transform JavaScript code into optimized machine code. Unlike traditional interpreters that execute code line by line, or ahead-of-time (AOT) compilers that compile the entire code before execution, JIT compilers compile code at runtime, which allows for dynamic optimizations based on the code's actual execution patterns.
Phases of Execution
Parsing: When JavaScript code is loaded, V8 parses the code and generates an Abstract Syntax Tree (AST), which represents the structure of the code in a tree format.
Ignition: The AST is then converted into bytecode, which is a lower-level, simpler set of instructions that is easier for the machine to understand. Initially, this bytecode is executed by V8's interpreter, Ignition, which allows for quick startup times.
Profiling: While the bytecode is being interpreted, V8 collects profiling data to identify "hot" functions—those that are called frequently or are computationally intensive.
Optimization: Hot functions are passed to V8's optimizing compiler, TurboFan. TurboFan uses the profiling data to make informed optimizations, such as inlining functions, eliminating unnecessary operations, and optimizing loops. It then compiles these functions into highly optimized machine code.
Deoptimization: If the assumptions made during the optimization phase prove to be incorrect (e.g., due to changes in the types of variables), V8 can deoptimize the code, reverting it back to bytecode. The code can be re-optimized later with updated assumptions.
Key Features
Inline Caching: V8 uses inline caching to speed up property access on objects. It remembers the locations of properties within objects to avoid repeated lookup operations.
Hidden Classes: V8 creates hidden classes (also known as "shapes" or "maps") for objects that have the same properties. This allows V8 to optimize the code by assuming that objects with...
