从 JSON 文件推断字符串文字类型

我正在读取一个大的 JSON 文件。
TypeScript 足够智能推断类型所有属性中除了一个.

一个简化的例子：

type Animal = 'bear' | 'cat' | 'dog';

const data = {
  name: 'Max',
  age: 3,
  animal: 'dog',
  // 100s other properties from JSON file...
};

let theName: string = data.name; // perfect
let theAge: number = data.age; // perfect
let theAnimal: Animal = data.animal; // Error: Type 'string' is not assignable to type 'Animal'

(链接到游乐场 https://www.typescriptlang.org/play?#code/C4TwDgpgBAggdgSwLYEMA2UC8UDkAjCFAJxygB9cBjFYUinAEwHsBzHAbgChPKm4BnYFAY0UWKAG9OUKHBRIIALlwBZFAA8cAGmlQULJVADMOmSkSo0yxq226A9PagBGAAyv%20UJsAAWEIlBgREyQRMAIEJ4AZsFIUABSAMoA8gByUFEIaBAAdHmcAL5cnNlCvhCp8oaCRAhwLOIiwCg5cgrsUI6B-lEQlMAlEGV%20MAbKcACuSAQB2E0t%20hAdXaG9-YPDEPDI6Mrblo2iOeY7aMtOAKJEwUTKACrg0Dg1dWxQCJ5w3nr8-Agscjw2SgwCYIMeuH26BwnCAA)

data.animal在几个地方使用，所以我试图避免使用as Animal到处。

解决这个问题的最佳方法是什么？
有什么简单的方法可以告诉代码data.animal is an Animal?

您可以使用总和类型并合并 2 个定义 - 数据的原始定义和动物：动物定义。

type Animal = 'bear' | 'cat' | 'dog';

// the keys your want to exert
type DataWithAnimal = { [P in 'animal']: Animal } ;

const data = {
  name: 'Max',
  age: 3,
  animal: 'dog',
  // 100s other properties from JSON file...
};

// original data type
type DataType = typeof data;

// merge the 2 type definitions
type Data = DataType & DataWithAnimal;

// cast old type to new type
const typeData: Data = data as Data;

let theName: string = typeData.name; // perfect
let theAge: number = typeData.age; // perfect
let theAnimal: Animal = typeData.animal; // also perfect