How to get property based union type from an array of objects


```js
const arr = [
  {
    property: 'one',
  },
  {
    property: 'two',
  },
] as const;

type Property = Pick<typeof arr[number], 'property'>['property'];
//   ^? type Property = 'one' | 'two'
```


Using mapped types to access object properties

```js
type Configuration = {
  'one': number;
  'two': string[];
  'three': () => void;
}

// ✅ right
const fn = (what: { [key in keyof Configuration ]: Configuration[key]}) => {
  if (what.one) {
    what.one.toFixed();
  }

  if (what.two) {
    what.two.slice(0, 1);
  }

  if (what.three) {
    what.three();
  }
}

// ❌ wrong
const fn2 = (what: Record<Key, Configuration[Key]>) => {
  if (what.one) {
    what.one.toFixed();
  }
}
```


Michal Zimmermann

typescript

How to get property based union type from an array of objects

Using mapped types to access object properties