# 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/yargs');
const argv = yargs(process.argv.slice(2)).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'`.
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