一、类型别名
TypeScript 提供了为类型注解设置别名的便捷语法，你可以使用 type SomeName = someValidTypeAnnotation 来创建别名，比如：
type Pet = 'cat' | 'dog';
let pet: Pet;
pet = 'cat'; // Ok
pet = 'dog'; // Ok
pet = 'zebra'; // Compiler error
二、基础知识
为了让大家能更好地理解并掌握 TypeScript 内置类型别名，我们先来介绍一下相关的一些基础知识。
2.1 typeof
在 TypeScript 中， typeof 操作符可以用来获取一个变量声明或对象的类型。
interface Person {
name: string;
age: number;
const sem: Person = { name: 'semlinker', age: 30 };
type Sem= typeof sem; // -> Person
function toArray(x: number): Array<number> {
return [x];
type Func = typeof toArray; // -> (x: number) => number[]
type K1 = keyof Person;
//
"name" | "age"
type K2 = keyof Person[];
//
"length" | "toString" | "pop" | "push" | "concat" | "join"
type K3 = keyof { [x: string]: Person };
//
string | number
function
loggingIdentity<T extends ILengthwise>
(arg: T): T {
console.log(arg.length);
return
arg;
在以上代码中，首先通过 keyof T 拿到 T 的所有属性名，然后使用 in 进行遍历，将值赋给 P ，最后通过 T[P] 取得相应的属性值。中间的 ? ，用于将所有属性变为可选。
interface Todo {
title: string;
description: string;
function updateTodo(todo: Todo, fieldsToUpdate: Partial<Todo>) {
return { ...todo, ...fieldsToUpdate };
const todo1 = {
title: "organize desk",
description: "clear clutter"
const todo2 = updateTodo(todo1, {
description: "throw out trash"
* Construct a type with a set of properties K of type T
type Record<K extends keyof any, T> = {
[P in K]: T;
const x: Record<Page, PageInfo> = {
about: { title: "about" },
contact: { title: "contact" },
home: { title: "home" }
* From T, pick a set of properties whose keys are in the union K
type Pick<T, K extends keyof T> = {
[P in K]: T[P];
type T0 = Exclude<"a" | "b" | "c", "a">; // "b" | "c"
type T1 = Exclude<"a" | "b" | "c", "a" | "b">; // "c"
type T2 = Exclude<string | number | (() => void), Function>; // string | number
type T0 = ReturnType<() => string>; // string
type T1 = ReturnType<(s: string) => void>; // void
type T2 = ReturnType<<T>() => T>; // {}
type T3 = ReturnType<<T extends U, U extends number[]>() => T>; // number[]
type T4 = ReturnType<any>; // any
type T5 = ReturnType<never>; // any
type T6 = ReturnType<string>; // Error
type T7 = ReturnType<Function>; // Error
type T0 = InstanceType<typeof C>; // C
type T1 = InstanceType<any>; // any
type T2 = InstanceType<never>; // any
type T3 = InstanceType<string>; // Error
type T4 = InstanceType<Function>; // Error
* Obtain the parameters of a function type in a tuple
type Parameters
<T extends (...args: any) => any> = T extends (...args: infer P) =>
any
? P : never;
type A = Parameters<() => void>; // []
type B = Parameters<typeof Array.isArray>; // [any]
type C = Parameters<typeof parseInt>; // [string, (number | undefined)?]
type D = Parameters<typeof Math.max>; // number[]
3.14 ConstructorParameters
ConstructorParameters<T> 的作用是提取构造函数类型的所有参数类型。它会生成具有所有参数类型的元组类型（如果 T 不是函数，则返回的是 never 类型）。
// node_modules/typescript/lib/lib.es5.d.ts
* Obtain the parameters of a constructor function type in a tuple
type ConstructorParameters<T extends new (...args: any) => any> = T extends new (...args: infer P) => any ? P : never;
type A = ConstructorParameters<ErrorConstructor>; // [(string | undefined)?]
type B = ConstructorParameters<FunctionConstructor>; // string[]
type C = ConstructorParameters<RegExpConstructor>; // [string, (string | undefined)?]
原文 https://semlinker.com/ts-utility-types/
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