Inside the V8 Engine: How JavaScript Runs at Lightning Speed

The V8 JavaScript Engine is an open-source JavaScript engine, built by Google, and most notably utilized by Google Chrome and Node.js. It is based on C++ and is fast, owing to Just-In-Time (JIT) compilation and good memory management.

How V8 Works

V8 compiles JavaScript code into machine code rather than interpreting line by line. This accelerates JavaScript execution significantly. The following is a step-by-step explanation of the process employed by V8:

1- Parsing the JavaScript Code

• The JavaScript source code is first parsed into an Abstract Syntax Tree (AST).

• A scanner/tokenizer breaks the code into tokens (keywords, identifiers, symbols).

• A parser converts these tokens into a tree-like structure (AST), which represents the structure of the code.

2- Ignition (Interpreter)

• The AST is then passed to the Ignition interpreter, which converts it into bytecode.

• Bytecode is an intermediate representation that is easier to execute than raw JavaScript source code.

• Ignition executes this bytecode initially.

3- TurboFan (JIT Compiler)

• As the code runs, V8 identifies frequently executed (hot) functions.

• These hot functions are compiled into highly optimized machine code by TurboFan.

• This machine code runs much faster than interpreted JavaScript.

4- Optimization & Deoptimization

• V8 continuously profiles the running code to optimize frequently used functions.

• If a function's behavior changes (e.g., due to dynamic typing in JavaScript), V8 may deoptimize it and fall back to bytecode execution.

5- Garbage Collection & Memory Management

• V8 uses an advanced Garbage Collector (GC) to manage memory.

• It uses the Orinoco garbage collector, which is a Generational GC:

• Young Generation: Stores short-lived objects. Old Generation: Stores long-lived objects.

• The GC runs in parallel to avoid blocking JavaScript execution.