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@arnesfield/cli

cli

Simple interface for the command line.

Provides a simple command-line interface using the Node.js readline module.

const { createCLI } = require('@arnesfield/cli');

const cli = createCLI();
cli.on('data', data => console.log('Hello %s!', data));
cli.start();

Installation

npm install @arnesfield/cli

Usage

Create a CLI using the createCLI function and start it with start(). Add and remove event listeners via the on and off methods.

// create the interface
const cli = createCLI();
// listen for data and do stuff
cli.on('data', data => {
  console.log('Hello %s!', data);
});
// start the CLI
cli.start();

Output:

> World
Hello World!

Input Flow

This flow is used for every input:

1. A line event is emitted by the readline interface.
2. Call rl.pause().
3. Parse input if a parser is provided and pass it to the data event listeners.
4. Call the error event listeners for each data event listener error.
5. Finally, call rl.resume() and rl.prompt(true).
6. Since rl.resume() is called, the next line in the queue is emitted and the flow repeats.

CLIOptions

You can pass options to createCLI(). You can pass your own readline Interface and a custom parser function.

interface CLIOptions<T> {
  /** The `readline` interface to use. */
  rl?: Interface;

  /** Custom parser for parsing raw input. */
  parser?(input: string): T | Promise<T>;
}

The parser option accepts a function to transform the input.

In the example below, we create a CLI with a parser that trims and splits the input by spaces.

const cli = createCLI({
  parser: input => input.trim().split(' ')
});
cli.on('data', data => {
  console.log('Array:', data);
});
cli.start();

Output:

> Hello World!
Array: [ 'Hello', 'World!' ]

The CLI object

interface CLI<T = string> {
  /** The `readline` interface. */
  readonly rl: Interface;

  /** Starts the CLI. Accepts data or input to parse. */
  start(): this;
  start(data: T, parse?: false): this;
  start(input: string, parse: true): this;

  /** Accepts data and emits the data to the listeners. */
  data(data: T): this;

  /** Accepts raw input to parse and emits the data to the listeners. */
  input(input: string): this;

  /** Calls `rl.prompt(true)` if not closed. */
  prompt(): this;

  /**
   * Ignores incoming `line` event data, and removes ignored
   * lines from `rl`'s `history` until `data` event is resolved.
   */
  ignore(ignore?: boolean): this;

  /** Adds listener. */
  on(event: 'data', listener: DataListener<T>): this;
  on(event: 'error', listener: ErrorListener): this;

  /** Removes listener. */
  off(event: 'data', listener: DataListener<T>): this;
  off(event: 'error', listener: ErrorListener): this;
}

Emit data events

You can emit data events through these methods:

cli.input(input); // accepts input to parse
cli.data(data); // accepts parsed input
cli.start(input, true); // accepts input to parse before starting
cli.start(data); // accepts parsed input before starting

Using cli.ignore()

The cli.ignore() method does the following:

1. Calls rl.resume().
2. Ignores incoming line event data including queued lines from rl.pause().
3. Removes ignored lines from rl's history.
4. Will automatically unignore after data event listeners are emitted and resolved.

A use case for cli.ignore() is when the data listener takes a while to finish (async) and you don't want to accept any input until the process has finished.

const cli = createCLI();
cli.on('data', async data => {
  // ignore incoming lines
  cli.ignore();
  console.log('Processing "%s"', data);
  await new Promise(resolve => setTimeout(resolve, 2000));
  console.log('Done "%s"', data);
});
cli.start();

After entering Hello World!, input foo, bar, baz while the listener is not yet resolved. Output:

> Hello World!
Processing "Hello World!"
foo
bar
baz
Done "Hello World!"