memo
```typescript
type JsonObject = { [ index: string ]: JsonValueTypes }
type JsonValueTypes = JsonObject | Array<any> | number | string | true | false | null;
type JsonType = JsonValueTypes;
const obj: JsonType = {
"foo": {
"bar": true
}
}
```
あとで読む
https://github.com/Microsoft/TypeScript/issues/1897