根据值类型过滤键子列表的接口键

Problem

给定一个被视为映射的 TypeScript 接口 （将唯一键类型与非唯一值类型相关），可以提取 映射到指定值类型的键类型？

作为一个具体的例子，从WindowEventMap in lib.dom.d.ts...

interface WindowEventMap 
    extends GlobalEventHandlersEventMap, WindowEventHandlersEventMap {
    "abort": UIEvent;
    "afterprint": Event;
    "beforeprint": Event;
    "beforeunload": BeforeUnloadEvent;
    "blur": FocusEvent;
    // ...
}

有一个内置运算符keyof获取所有密钥：

type FullKeyList = keyof WindowEventMap;
// gives: FullKeyList = "'abort' | 'afterprint' | 'beforeprint' | ..and 93 more"

是否有一些表达式可以仅过滤映射到值类型的键KeyboardEvent?:

// Goal:
type SubKeyList = SomeExpression<WindowEventMap, KeyboardEvent>;
// would give: SubKeyList = "'keyup' | 'keypress' | 'keydown'"

解决方案尝试

TypeScript 具有条件类型表达式：

T extends U ? X : Y

所以这是一个合理的尝试：

type Filter<K extends keyof M, V, M> = M[K] extends V ? K : never;

它过滤单个类型：

// Passes this test:
type FilteredExample1 = Filter<'keyup', KeyboardEvent, WindowEventMap>;
// gives FilteredExample1 = "'keyup'"

// Passes this test:
type FilteredExample2 = Filter<'blur', KeyboardEvent, WindowEventMap>;
// gives FilteredExample2 = "never"

它可以过滤类型的联合并返回一个新的联合吗？开始看起来不错：

// Passes this test:
type FilteredUnionExample1 = Filter<'keyup' | 'keydown', KeyboardEvent , WindowEventMap>;
// gives FilteredUnionExample1 = "'keyup' | 'keydown'"

但如果联盟的一名或多名成员失败，联盟就会失败：

// Fails this test:
type FilteredUnionExample2 = Filter<'keyup' | 'keydown' | 'blur', KeyboardEvent, WindowEventMap>;
// gives FilteredUnionExample2 = "never" (and not sub-union "'keyup' | 'keydown'")

// And so, it also fails the end-goal usage:
type AllKeysUnion = keyof WindowEventMap;
type FilteredUnionExample3 = Filter<AllKeysUnion, KeyboardEvent , WindowEventMap>;
// gives FilteredUnionExample3 = "never" (not sub-union "'keyup' | 'keypress' | 'keydown'")

这个问题有解决办法吗？

我通常称之为KeysMatching:

type KeysMatching<T, V> = {[K in keyof T]: T[K] extends V ? K : never}[keyof T];

type SubKeyList = KeysMatching<WindowEventMap, KeyboardEvent>
// type SubkeyList = "keydown" | "keypress" | "keyup"

Playground 代码链接 https://www.typescriptlang.org/play?jsx=3#code/C4TwDgpgBA0hIGcCyBDYBjAFgSwHYHMAeAFQBooA1APigF4oBvAbRijygGt4B7AMymIBdAFwCWgqBAAewCLgAmCSlAD8sKKNwQAbhABOAXyZcQfAYIDcAWABQt0JCgBlAK4AjOCAAy2BMDqw8MhoWHhEAOp48twA7gCiurjAqGDknm7cKHryCXLAVLYA9IVQDtCubiY+fgEARCbRMbi1UAA+UPXwYHoQCAgt7Z0gLmC1QA