# 🛩 v8 Engine

3 min read, 540 words v8 engine javascript compiler runtime

v8 javascript engine logo

v8 is Javascript runtime in chrome and nodejs

Asynchronous IO is based in Event Loops
- use libuv for that
100k lines of JS and C++ code, glue between libuv and v8
- inbuilt node modules, standard modules

v8 what?

called by many names

v8 Js Runtime js Engine compiler virtual machine

Just In Time compiler
- compile a little bit and run, compile a little bit and run it automated
- speculative optimization
written in C++
Implements javascript according to ECMA Specification
- Everytime there are modifications in specifactions, they are added to runtime
Garbage Collection
WebAssembly is also a part of v8 starting 2019
- https://www.infoq.com/news/2020/02/v8-webassembly-simd/ (opens new window)
- https://www.google.com/search?q=javascript+v8&newwindow=1&sxsrf=ALeKk03qxPq35f3dJ7-IpoVOJFVTlheQSA:1596773429800&source=lnms&tbm=nws&sa=X&ved=2ahUKEwj2n8fInIjrAhVDNOwKHUlvCq0Q_AUoBHoECEIQBg&biw=1294&bih=641 (opens new window)

not in v8

DOM data structure is NOT the responsibility of js engine. Its created by browser application
No File System access. libuv is used for FSOperations
console, responsibility of node or chrome app to provide it.

Majority of v8 team in Munich, Germany
Same release schedule as chrome, every 6 weeks
v8 API is a part of ECMA Script specification which is exposed to node or chrome
v8 compiler pipeline change - support for node 8
- Full Cogent and crankshaft -> ignition and turbofan
- ABI - Application Binary Interface guarentee to support node LTS version for stability
- node v8 integration bot
since node 7 use devtools and CDP protocol for debugging
node is a first class citizen in v8 now

# 🗃 Heap vs Stack

the standard distinguishes automatic and dynamic storage duration. Local variables have automatic storage duration and compilers store them on the stack. Objects with dynamic memory allocation (created with new) are stored on the free store, conventionally referred to as the heap. In languages that are not garbage-collected, objects on the heap lead to memory leaks if they are not freed.

# Who uses it?

node
electron

# Official documentation

If you are a C++ developer you can use v8 in your Application
How javascript is used?
- Manupulate DOM
- v8 exposes all datatypes, operators, functions and objects as specified in ECMAScript standard
Uses Code Caching Technique
- cached data is availble to seperate v8 instance as well
- v8::ScriptCompiler::Source::GetCachedData

JIT Units	Codenames
Garbage Collector	Orinoco
Baseline Compiler	Ignition
Optimization Compiler	Turbo Fan

# 📉 Tracing

node --trace-events-enabled tracing.js

How to view, read trace?
- Google chrome have built in trace viewer
- chrome://tracing

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