使用it.each测试类成员时如何避免any类型转换？

方法一：用keyof Foo约束属性类型，结合类型断言 #

把property的类型明确为keyof Foo，让TypeScript识别它是Foo的合法属性，无需转成any。如果偏好数组形式的test.each，可以直接添加类型约束：

class Foo {
    bar = "string"
    baz = "another-string"
}

type FooProperty = keyof Foo;

test.each<{ property: FooProperty; value: string }>([
  { property: "bar", value: "string" },
  { property: "baz", value: "another-string" },
])("$property maps to $value", ({ property, value }) => {
  const foo = new Foo();
  expect(foo[property]).toEqual(value); // 类型安全，无需any
});

如果坚持用模板字符串形式的test.each，给参数手动加类型注解即可：

test.each`
  property  | value
  ${"bar"}  | ${"string"}
  ${"baz"}  | ${"another-string"}
`("$property maps to $value", ({ property, value }: { property: keyof Foo; value: string }) => {
  const foo = new Foo();
  expect(foo[property as keyof Foo]).toEqual(value);
});

方法二：用类型守卫确保属性合法性 #

先校验property是否属于Foo的合法属性，TypeScript会自动缩小类型范围，无需强制转换：

class Foo {
    bar = "string"
    baz = "another-string"
}

function isFooProperty(key: string): key is keyof Foo {
  return key in new Foo();
}

test.each`
  property  | value
  ${"bar"}  | ${"string"}
  ${"baz"}  | ${"another-string"}
`("$property maps to $value", ({ property, value }) => {
  const foo = new Foo();
  if (isFooProperty(property)) {
    expect(foo[property]).toEqual(value); // 类型安全
  } else {
    fail(`Invalid property: ${property}`);
  }
});

方法三：给类添加索引签名（不推荐，仅适用于属性类型统一的场景） #

如果可以修改Foo类，添加索引签名让TypeScript允许字符串索引访问：

class Foo {
    bar = "string"
    baz = "another-string"
    [key: string]: string; // 添加索引签名
}

test.each`
  property  | value
  ${"bar"}  | ${"string"}
  ${"baz"}  | ${"another-string"}
`("$property maps to $value", ({ property, value }) => {
  const foo = new Foo();
  expect(foo[property]).toEqual(value);
});

注意：如果Foo存在非string类型的属性，这种方式会导致类型冲突，谨慎使用。

内容的提问来源于stack exchange，提问作者Ben Wainwright