matthyk / extra-typings

Infer strong typings for commander options and action handlers

extra-typings for commander

This package offers TypeScript typings for commander which infer strong types for:

• all the parameters of the action handler, including the options
• options returned by .opts()

The runtime is supplied by commander. This package is all about the typings.

Usage

• install @commander-js/extra-typings using your preferred package manager
• install commander, if not already installed (peer dependency)
• in code import from @commander-js/extra-typings instead of commander

The installed version of this package should match the major and minor version numbers of the installed commander package, but the patch version number is independent (following pattern used by Definitely Typed).

Credit: this builds on work by @PaperStrike in tj/commander.js#1758

Limitations

• the generics lead to some noisy types visible in editor and errors
• some minor code changes required for subclasses of Command, Argument, or Option (see subclass.test-d.ts)
  • chaining methods which do type inference return base class rather than this
  • subclass of Command returns base class not subclass from .command(name)
  • type parameter needed for class declaration of subclass of Option and Argument

Usage tips

The types are built up as the options and arguments are defined. The usage pattern for action handlers is easy. Just chain the action handler after the options and arguments.

import { program } from '@commander-js/extra-typings';

program.command('print')
  .argument('<file>')
  .option('--double-sided')
  .action((targetFile, options) => {
    // command-arguments and options are fully typed
  });

For working with a single command without an action handler, the configuration need to be done at the same time as the variable is declared.

import { Command } from '@commander-js/extra-typings';

// broken pattern
const program = new Command(); // program type does not include options or arguments
program.option('-d, --debug'); // adding option does not change type of program
const options = program.opts(); // dumb type

import { Command } from '@commander-js/extra-typings';

// working pattern
const program = new Command()
  .option('-d, --debug'); // program type includes chained options and arguments
const options = program.opts(); // smart type

Use a "const assertion" on the choices to narrow the option type from string:

const program = new Command()
  .addOption(new Option('--drink-size <size>').choices(['small', 'medium', 'large'] as const))
  .parse();
const drinkSize = program.opts().drinkSize; // "small" | "medium" | "large" | undefined