如何在 Typescript 中获取输入的 Object.entries() 和 Object.fromEntries？

Question

当我在打字稿中使用Object.fromEntries(entries)orObject.entires(obj)来表示类型/常量entries数组或objt对象时，我会丢失类型any或广泛类型。

在某些情况下，我可以手动分配通用类型（例如Record<string, number>），但是设置每对/键的类型很繁琐。

这是我想要的一个例子。

类型化 Object.fromEntries(entries)

const myArrayOfPairs = [["a", 5], ["b", "hello"], ["c", false]] as const;

// The type of the following is "any"
const myTypelessObject = Object.fromEntries(myArrayOfPairs);

// I want the type of this one to be: { a: 5; b: "hello"; c: false; }
const myTypedObject = createTypedObjectFromEntries(myArrayOfPairs); 

类型化 Object.entries(obj)

const myOldObject = {
    x: 6,
    y: "apple",
    z: true
};

// The type of the following is [string, string | number | boolean][]
const myEntries = Object.entries(myOldObject);

// I want the type of this one to be more specific.
// i.e.: (["x", number] | ["y", string] | ["z", boolean])[]
const myTypedEntries = getTypedObjectEntries(myOldObject);

Answer 1

Object.Entries(obj) -- 对象到键值对数组

这一个相对简单。使用[K in keyof OBJ_T]可以获取键，并OBJ_T[K]给出相对值。

这是它的一个简单实现：

// ~~~~~~~~~~~~~~~~~~~~~~~~ Utils ~~~~~~~~~~~~~~~~~~~~~~~~

type ObjectType = Record<PropertyKey, unknown>;
type PickByValue<OBJ_T, VALUE_T> // From /sf/answers/3860710031/
    = Pick<OBJ_T, { [K in keyof OBJ_T]: OBJ_T[K] extends VALUE_T ? K : never }[keyof OBJ_T]>;
type ObjectEntries<OBJ_T> // From /sf/answers/4209946681/
    = { [K in keyof OBJ_T]: [keyof PickByValue<OBJ_T, OBJ_T[K]>, OBJ_T[K]] }[keyof OBJ_T][];

// ~~~~~~~~~~~~~~~~~~~~ Typed Function ~~~~~~~~~~~~~~~~~~~~

function getTypedObjectEntries<OBJ_T extends ObjectType>(obj: OBJ_T): ObjectEntries<OBJ_T> {
    return Object.entries(obj) as ObjectEntries<OBJ_T>;
}

// ~~~~~~~~~~~~~~~~~~~~~~~~~ Test ~~~~~~~~~~~~~~~~~~~~~~~~~

const myOldObject = {
    x: 6,
    y: "apple",
    z: true
};

const myTypelessEntries = Object.entries(myOldObject); // type: [string, string | number | boolean][]

const myTypedEntries = getTypedObjectEntries(myOldObject);
type myTypedEntiresType = typeof myTypedEntries;  // type: (["x", number] | ["y", string] | ["z", boolean])[]

TS游乐场。请注意，您需要es2019成为 Configs 中的目标。

Object.fromEntries(entries) -- 对象的键值对数组

这是一个更具挑战性的事情。

您需要首先使用 提取内部数组对infer，然后使用通用实用UnionToIntersection程序类型合并结果。

这是我能想到的最好的：

// ~~~~~~~~~~~~~~~~~~~~~~~~ Utils ~~~~~~~~~~~~~~~~~~~~~~~~

// Data Types
type EntriesType = [PropertyKey, unknown][] | ReadonlyArray<readonly [PropertyKey, unknown]>;

// Existing Utils
type DeepWritable<OBJ_T> = { -readonly [P in keyof OBJ_T]: DeepWritable<OBJ_T[P]> };
type UnionToIntersection<UNION_T> // From /sf/answers/3526270051/
    = (UNION_T extends any ? (k: UNION_T) => void : never) extends ((k: infer I) => void) ? I : never;

// New Utils
type UnionObjectFromArrayOfPairs<ARR_T extends EntriesType> =
    DeepWritable<ARR_T> extends (infer R)[] ? R extends [infer key, infer val] ? { [prop in key & PropertyKey]: val } : never : never;
type MergeIntersectingObjects<ObjT> = {[key in keyof ObjT]: ObjT[key]};
type EntriesToObject<ARR_T extends EntriesType> = MergeIntersectingObjects<UnionToIntersection<UnionObjectFromArrayOfPairs<ARR_T>>>;

// ~~~~~~~~~~~~~~~~~~~~~ Typed Functions ~~~~~~~~~~~~~~~~~~~~~

function createTypedObjectFromEntries<ARR_T extends EntriesType>(arr: ARR_T): EntriesToObject<ARR_T> {
    return Object.fromEntries(arr) as EntriesToObject<ARR_T>;
}

// ~~~~~~~~~~~~~~~~ Test for entries->object ~~~~~~~~~~~~~~~~~

const myArrayOfPairs = [["a", 5], ["b", "hello"], ["c", false]] as const;

const myTypelessObject = Object.fromEntries(myArrayOfPairs); // type: any

const myTypedObject = createTypedObjectFromEntries(myArrayOfPairs);
type myTypedObjectType = typeof myTypedObject; // type: { a: 5; b: "hello"; c: false; }

TS游乐场

Answer 2

现在，使用新的 .TypeScript 5 可以更轻松地实现这一点const Type Parameter。

\n

//\n// Object.fromEntries\n//\n\nconst typeSafeObjectFromEntries = <\n  const T extends ReadonlyArray<readonly [PropertyKey, unknown]>\n>(\n  entries: T\n): { [K in T[number] as K[0]]: K[1] } => {\n  return Object.fromEntries(entries) as { [K in T[number] as K[0]]: K[1] };\n};\n\nconst myObject = typeSafeObjectFromEntries([\n  ["a", 5],\n  ["b", "hello"],\n  ["c", false],\n]); // { a: 5; b: "hello"; c: false } \xe2\x9c\x85\n\n//\n// Object.entries\n// (add const param for less broader types (ie. string -> "apple") -> const T extends Record<PropertyKey, unknown>)\n//\n\nconst typeSafeObjectEntries = <T extends Record<PropertyKey, unknown>>(\n  obj: T\n): { [K in keyof T]: [K, T[K]] }[keyof T][] => {\n  return Object.entries(obj) as { [K in keyof T]: [K, T[K]] }[keyof T][];\n};\n\nconst myEntries = typeSafeObjectEntries({ x: 6, y: "apple", z: true });\n// ["x", number] | ["y", string] | ["z", boolean])[] \xe2\x9c\x85\n// with const param: (["x", 6] | ["y", "apple"] | ["z", true])[] \xe2\x9c\x85\n

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TypeScript 游乐场

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