repl-ns

Namespace for REPL driven development for TypeScript/JavaScript. Inspired by Clojure namespaces. Currently tested on Node.js, but potentially can be used on any JavaScript runtime (Deno, Bun, Browser and so on...)

Why REPL driven development?

TL;DR Because it fastest, glad and fun way to develop software. Clojure guys approve it

Node.js development process evolved gradually. At the beginning was nothing, and developers restarted node.js from scratch manually for code testing. Then some automation appears nodemon. Fine! Now I can relax from boring Ctrl+C -> UP -> Enter process. But it's not enough! Restarting node.js process from scratch is very expensive!

• Need to require in runtime all project files. Yes! All this hundreds files of your 3+ years old monolith 😊
• Seems you have TypeScript too. Need to transpile all this kind with additional time wasting (Yeah! Say hello to ts-node perf tweak and all new TypeScript compilers, which written on Rust/C++/Go 😀)
• And establish DB connection too
• And establish Kafka/RabbitMQ/SQS connection too
• And establish Redis connection too
• And start HTTP server too

☝️ And all this seconds wasting process for just testing one line of code, that I change? Maybe better "restart" one function instead whole process, where this line of code was changed?

How to use (example)

Run your node.js program with --inpsect flag. Exposed inspect protocol will be used for REPL driven development.

Then organize code in your project using REPL driven development friendly style:

some-namespace.ts

import { ns } from 'repl-ns';

export const someNS = ns('some-namespace', {
  fn() {
    return 1 + 1
  },
});

And call namespace related functions anywhere:

import { someNS } from 'src/some-namespace';

someNS().fn() // 2

Now you can replace someNS.fn implementation in runtime without restarting node.js process. Just edit some-namespace.ts

- return 1 + 1
+ return 2 + 2

and use, for example, node-remote-repl - node-remote-repl some-namespace.ts Now anywhere someNS().fn() // will return 4 BTW, setup IDE for REPL driven development VSCode example

Awesome! 🦄 Now fastest REPL driven development with node.js at your fingertips

Detailed example

import { ns } from 'repl-ns';

export const someNS = ns('some-namespace', {
  fn() {
    return 1 + 1 // functions always will be replaced in REPL
  },
  
  obj: {foo: 'bar'} // objects will be preserved in REPL by default (for stateful)
}, {
  forceRewrite: true, // if you want force replace objects too, this option will be helpful
  rewriteKeys: ['obj'], // or you can pick specific items for replacing
  async before(props) {
    // optional before hook namespace initialization
    // old namespace payload will be passed in props (if exists)
    // here you can close DB connection, stop HTTP server and so on
  },
  async after(props) {
    // optional after hook namespace initialization
    // new namespace payload will be passed in props
    // here you can establish DB connection, start HTTP server and so on
  },
  sync: true // pass sync: true if your namespace has totally sync behaviour
});

await someNS.ready // promise for ready state of namespace (before, after hooks executed yet)

Real projects used repl-ns

You can explain code of projects:

• ytdl-tui - TUI for downloading YouTube videos, totally writen with REPL driven development approach using repl-ns

Caveats

Avoid using relative paths in your project:

import { someNS } from '../../some-namespace';

Because REPL code is run in root and can't detect relative paths

Use non-relative paths instead:

import { someNS } from 'src/some-namespace';

Projects, which helps with non-relative paths:

• tsconfig-paths
• tsc-alias