bandersnatch

bandersnatch

Super lightweight and friendly CLI framework for Node.js.

🚧 alpha version

Features

• ➰ Built-in REPL
• 💬 Prompts for missing arguments
• ➡ Autocompletes arguments, options and values
• 🤯 Fully typed
• ⚡ Uses the power of yargs & inquirer

It's built in TypeScript and while it's of course possible to write your app with JavaScript, you're missing out on some very handy type hints.

We don't have a generator, auto-updater and we don't make any decisions for you (apart from using inquirer for prompts). This makes bandersnatch pretty easy and intuitive to work with.

Table of contents

• Getting started
  • Installation
  • Simple
  • REPL
  • Prompt
• API
  • program(description)
    • program.add(command)
    • program.default(command)
    • program.prompt(prompt)
    • program.withHelp()
    • program.withVersion()
    • program.fail(function)
    • program.eval(command)
    • program.run(command)
    • program.repl()
  • command(name, description)
    • command.argument(name, description, options)
    • command.option(name, description, options)
    • command.command(command)
    • command.default()
    • command.action(function)
  • runner
    • runner.print(printer)
    • runner.then(function)
    • runner.catch(function)
    • runner.print(printer)
  • printer
    • printer.write(string)
    • printer.error(Error)
• Bundle
• Todo
• Contributing
• License

Getting started

Installation

# Add dependency
yarn add bandersnatch

Simple

Now create a simple app echo.ts:

import { program, command } from 'bandersnatch'

const echo = command('echo', 'Echo something in the terminal')
  .argument('words', 'Say some kind words', { variadic: true })
  .action(args => args.words.map(word => `${word}!`).join(' '))

program()
  .default(echo)
  .run()

And run with:

$ ts-node echo.ts Hello world
Hello! world!

👆 Assuming you have ts-node installed.

REPL

Let's dive right into some more features. This simple app has a single default command which pretty prints JSON input. When invoked without input, it'll show an interactive prompt:

import { program, command } from 'bandersnatch'

const app = program('JSON pretty printer').default(
  command()
    .argument('json', 'Raw JSON input as string')
    .option('color', 'Enables colorized output', { type: 'boolean' })
    .action(async args => {
      const json = JSON.parse(args.json)
      args.color
        ? console.dir(json)
        : console.log(JSON.stringify(json, undefined, 4))
    })
)

process.argv.slice(2).length ? app.run() : app.repl()

And run with:

$ ts-node pretty.ts
> [0,1,1,2,3,5]
[
    0,
    1,
    1,
    2,
    3,
    5
]

Now, try typing [0,1,1,2,3,5] --c and then hit TAB. 😊

Prompt

Bandersnatch can also ask a user for input if arguments were not provided on the command line:

import { program, command } from 'bandersnatch'

const cmd = command()
  .argument('name', "What's your name?", {
    prompt: true
  })
  .argument('question', "What's your question?", {
    prompt: true
  })
  .action(args => `Hi ${args.name}, the answer to "${args.question}" is 42.`)

program('Ask me anything')
  .default(cmd)
  .run()

And run with:

$ ts-node ama.ts --name Joram
? What's your question? What is everything in ASCII?
Hi Joram, the answer to "What is everything in ASCII?" is 42.

When you omit the --name part, the program will also prompt for it.

---

ℹ More examples in the examples directory.

API

All methods are chainable unless the docs mention otherwise.

program(description)

Creates a new program.

• Description (string, optional) is used in --help output.

program.add(command)

Adds a command to the program.

program().add(command(...))

program.default(command)

Adds a default command to the program. Shorthand for:

program().add(command(...).default())

program.prompt(prompt)

Use this prompt prefix (string, required) when in REPL mode.

program.withHelp()

Adds help and --help to program which displays program usage information.

program.withVersion()

Adds version and --version to program which displays program version from package.json.

program.fail(function)

Use custom error handler. Function will be called with 4 arguments:

• Message (string) will contain internal message about e.g. missing arguments
• Error (Error) is only set when an error was explicitly thrown
• Args (array) contains program arguments
• Usage (string) contains usage information from --help

program.eval(command)

Uses process.argv or passed in command (string, optional) to match and execute command. Returns runner instance.

program()
  .add(command(...))
  .eval()

program.run(command)

Shorthand for eval().print().

program()
  .add(command(...))
  .run()

program.repl()

Start a read-eval-print loop.

program()
  .add(command(...))
  .repl()

command(name, description)

Creates a new command.

• Name (string, optional) is used to invoke a command. When not used as default command, name is required.
• Description (string, optional) is used in --help output.

command.argument(name, description, options)

Adds a positional argument to the command.

• Name (string, required) is used to identify the argument. Can also be an array of strings, in which case subsequent items will be treated as command aliases.
• Description (string, optional) is used in --help output.
• Options can be provided to change the behaviour of the argument. Object with any of these keys:
  • optional (boolean) makes this argument optional.
  • variadic (boolean) eagerly take all remaining arguments and parse as array. Only valid for last argument.
  • ...

command.option(name, description, options)

Adds an option to the command.

• Name (string, required) is used to identify the option.
• Description (string, optional) is used in --help output.
• Options (OptionOptions) can be provided to change the behaviour of the option. Object with any of these keys:
  • alias (string or array of strings) alias(es) for the option key.
  • ...

command.command(command)

Adds a sub-command to the command.

command.default()

Mark command as default. Default commands are executed immediately and don't require a name.

command.action(function)

Function to execute when command is invoked. Is called with one argument: an object containing key/value pairs of parsed arguments and options.

runner

Returned from program().eval(), can't be invoked directly.

runner.print(printer)

Prints resolved and rejected command executions to the terminal. Uses the built-in printer if invoked without arguments.

const runner = program()
  .default(
    command().action(() => {
      throw new Error('Test customer printer')
    })
  )
  .eval()

runner.print({
  write(str: any) {
    str && console.log(str)
  },
  error(error: any) {
    console.error(`${red('‼')} ${bgRed(error)}`)
  }
})

runner.then(function)

Function is invoked when command handler resolves.

runner.catch(function)

Function is invoked when command handler rejects.

runner.print(printer)

Attaches a printer to the runner. Uses a default printer unless called with a custom printer argument.

printer

Used by runner, can't be invoked directly.

printer.write(string)

Handles output. Prints to stdout by default.

printer.error(Error)

Handles errors. Prints stack trace to stderr by default.

Bundle

There are many options to bundle your application for distribution. We'll discuss a common pattern.

ℹ An example can be found in the examples/bundle directory.

Init a package.json if needed:

mkdir echo && cd echo
yarn init

Install dependencies:

yarn add bandersnatch
yarn add typescript pkg --dev

And create an example app in src/cli.ts:

import { program, command } from 'bandersnatch'

export default program()
  .withHelp()
  .default(
    command('echo', 'Echo something in the terminal')
      .argument('words', 'Say some kind words', { variadic: true })
      .action(console.log)
  )

Building your app with TypeScript is very powerful, but runtime compilation is slow so we compile the code ahead of time.

Add a tsconfig.json, similar to:

{
  "include": ["./src"],
  "compilerOptions": {
    "target": "es2017",
    "module": "commonjs",
    "lib": ["es2017"],
    "declaration": true,
    "outDir": "lib",
    "rootDir": "src",
    "strict": true,
    "allowSyntheticDefaultImports": true,
    "esModuleInterop": true,
    "moduleResolution": "node"
  }
}

Add these scripts to your package.json:

 {
   "name": "echo",
   "version": "1.0.0",
   "main": "index.js",
   "license": "MIT",
+  "scripts": {
+    "prepublishOnly": "yarn build",
+    "build": "tsc",
+  },
   "dependencies": {
     "bandersnatch": "^1.0.0-alpha.2"
   },
   "devDependencies": {
     "pkg": "^4.4.2",
     "typescript": "^3.7.3"
   }
 }

And compile now by running yarn build.

Next, we need to create a simple entrypoint echo.js, which can be run with node:

#!/usr/bin/env node

require('./lib/cli').default.run()

To run your app, users may want to run yarn global add echo. For this to work, we need to make a small adjustment to package.json:

 {
   "name": "echo",
   "version": "1.0.0",
-  "main": "index.js",
+  "bin": "echo.js",
+  "files": [
+    "lib"
+  ],
   "license": "MIT",
   "scripts": {
     "prepublishOnly": "yarn build",
     "build": "tsc",
   },
   "dependencies": {
     "bandersnatch": "^1.0.0-alpha.2"
   },
   "devDependencies": {
     "pkg": "^4.4.2",
     "typescript": "^3.7.3"
   }
 }

You can now npm publish.

To create a binary (your app with Node.js bundled), add this script to package.json:

 {
   "name": "echo",
   "version": "1.0.0",
   "bin": "echo.js",
   "files": [
     "lib"
   ],
   "license": "MIT",
   "scripts": {
     "prepublishOnly": "yarn build",
     "build": "tsc",
+    "bundle": "yarn build && pkg -t host ."
   },
   "dependencies": {
     "bandersnatch": "^1.0.0-alpha.2"
   },
   "devDependencies": {
     "pkg": "^4.4.2",
     "typescript": "^3.7.3"
   }
 }

👆 Omit -t host to create binaries for all platforms.

Run yarn bundle and then ./echo --help. 💪

Optionally deploy to GitHub, S3, etc. using your preferred CD method if needed.

Todo

• Better code coverage
• Choices autocompletion in REPL mode

Contributing

Contributions are very welcome. Please note this project is in a very early stage and the roadmap is a bit foggy still...

# Clone and install
git clone [e-mail]:hongaar/bandersnatch.git
cd bandersnatch
yarn

# Run an example
yarn start examples/simple.ts

Please use conventional commits.

License

Copyright (c) 2019 Joram van den Boezem. Licensed under the MIT license.

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Inspired by vorpal