jiahao-si / learn-just-code

a very small v8 javascript runtime for linux only

Just

A very small v8 javascript runtime for linux only

Build and Run

Currently working on modern linux (debian/ubuntu and alpine tested) on x86_64

# download and run the build script
sh -c "$(curl -sSL https://raw.githubusercontent.com/just-js/just/current/install.sh)"
# install just binary to /usr/local/bin
make -C just install
# export the just home directory
export JUST_HOME=$(pwd)/just
export JUST_TARGET=$JUST_HOME
# if you don't want to install, add JUST_HOME to SPATH
export PATH=$PATH:$JUST_HOME
# run a shell
just

Create a new Application

# initialise a new application in the hello directory
just init hello
cd hello
# build hello app
just build hello.js --clean --static
./hello

Command Line Options

Run a Just shell/repl

just

Pipe a script to stdin

cat hello.js | just --

Eval some Javascript passed as an argument

just eval "just.print(just.memoryUsage().rss)"

Run a script

just hello.js

Initialise a new project and build it

just init hello
cd hello
just build

Clean a built project

just clean

Documentation

Coming soon...

Philosophy/Goals

• small, secure, robust and performant js runtime for linux
• small codebase. easy to understand and hack
• very simple layer on top of system calls, v8 and c/c++ standard libraries
• minimal use of classes/function templates and OO - "c" in javascript
• favour return codes over exceptions
• platform for building system software on linux in javascript
• as close to native performance as possible
• secure by default
• avoid abstraction as much as possible. abstractions can be built in userland
• commonjs modules, no support for ES modules
• non-async by default - can do blocking calls and not use the event loop
• event loop in JS-land. full control over epoll api
• small standard library - leave as much to userland as possible. focus on primitives needed to build higher level abstractions
• useful as a teaching/learning platform for linux system programming and learning more about javascript and v8 internals
• small number of source files
• minimal dependencies - g++ and make only
• keep LOC as small as possible < 5k
• allocate as little as possible on v8 heap