# TypeScript usage examples

The TypeScript definitions take into account yargs' `type` key and the prescense of
`demandOption`/`default`.

The following `.options()` definition:

```typescript
#!/usr/bin/env node
import yargs = require('yargs');

const argv = yargs.options({
  a: { type: 'boolean', default: false },
  b: { type: 'string', demandOption: true },
  c: { type: 'number', alias: 'chill' },
  d: { type: 'array' },
  e: { type: 'count' },
  f: { choices: ['1', '2', '3'] }
}).argv;
```

Will result in an `argv` that's typed like so:

```typescript
{
  [x: string]: unknown;
  a: boolean;
  b: string;
  c: number | undefined;
  d: (string | number)[] | undefined;
  e: number;
  f: string | undefined;
  _: string[];
  $0: string;
}
```


You will likely want to define an interface for your application, describing the form that
the parsed `argv` will take:

```typescript
interface Arguments {
  [x: string]: unknown;
  a: boolean;
  b: string;
  c: number | undefined;
  d: (string | number)[] | undefined;
  e: number;
  f: string | undefined;
}
```

To improve the `choices` option typing you can also specify its types:

```typescript
type Difficulty = 'normal' | 'nightmare' | 'hell';
const difficulties: ReadonlyArray<Difficulty> = ['normal', 'nightmare', 'hell'];

const argv = yargs.option('difficulty', {
  choices: difficulties,
  demandOption: true
}).argv;
```

`argv` will get  type `'normal' | 'nightmare' | 'hell'`.