V8 Reference

Online

This project is an API reference for Google's open-source v8 JavaScript engine.

• Install
• Core components
  • Mental model
  • Compiler pipeline
• Further readings
  • Articles
  • Videos

Install

1. Fetch the latest version v8 source code:

   $ git submodule init
   $ git submodule foreach git pull

2. Download doxygen binaries into doxygen directory.

3. Run command for generating documentations:

   $ ./doxygen/doxygen.exe

4. Done. All output HTML files are in the docs directory.

Core components

Mental model

Recommend: You don't know JS yet - compiling code

JavaScript is in fact parsed/compiled in a separate phase before execution begins. Scope is primarily determined during compilation.

In class compiler theory, a program is processed by a compiler in three basic stages:

1. Tokenizing/Lexing: breaking up a string of characters into meaningful (to the language) chunks, called tokens.

2. Parsing: taking a stream(array) of tokens and turning it init a tree of nested elements. This is called an abstract syntax tree(abbr, AST).

3. Code generation: taking an AST and turning it into executable code.

Compiler pipeline

related

• baseline compiler(as an interpreter) is called Ignition

• optimizing compiler is called TurboFan.

Further readings

Articles

• You don't known JS yet - Compiled vs. Interpreted

Videos

• JavaScript engines - how do they even?

  • Just in time compilation, abbr as JIT, 即时编译, just compiling the source code just in time as we need it

  • re-compile hot functions with type information from previous execution, de-optimize if the type has changed^#

    虽然 JS 是动态类型，但 v8 内部仍然是根据类型信息来优化代码实现 JIT 优化。^#

    How to optimize JS code with a concrete example

  • As a engine-level performance tip, always construct the same type of objects.^#

    function load(obj: { x: number, a: number, b: number}) {
      return obj.x
    }
    
    load(x: undefined, a: 3, b: 9)
    load(x: 3, a: undefined, b: 9)
    load(x: 4, a: 7, b: undefined)

  • Write code that looks like statically typed.

    Because JIT optimization depends on type information.

• JavaScript Engine Internals for JavaScript Developers

• JavaScript engine fundamentals: optimizing prototypes

• JavaScript engine fundamentals: Shapes and Inline Caches