類類型

寫法：

export interface ConstructorOf<T> {
    new(...args: any[]): T;
}

應用：

class BeeKeeper {
  hasMask: boolean = true;
}
 
class ZooKeeper {
  nametag: string = "Mikle";
}
 
class Animal {
  numLegs: number = 4;
}
 
class Bee extends Animal {
  keeper: BeeKeeper = new BeeKeeper();
}
 
class Lion extends Animal {
  keeper: ZooKeeper = new ZooKeeper();
}

function createInstance<A extends Animal>(c: ConstructorOf(A)): A {
  return new c();
}

createInstance(Lion).keeper.nametag;
createInstance(Bee).keeper.hasMask;

函數返回類型

寫法：

type ReturnType<T extends (...args: any[]) => any> = T extends (...args: any[]) => infer R ? R : any;

參數類型

寫法：

type Parameters<T> = T extends (...args: infer R) => any ? R : any;

應用：

type T0 = Parameters<() => string>;  // []
type T1 = Parameters<(s: string) => void>;  // [string]
type T2 = Parameters<(<T>(arg: T) => T)>;  // [unknown]

類型推導infer

參考

https://blog.csdn.net/KlausLily/article/details/108878205

題目：https://github.com/LeetCode-OpenSource/hire/blob/master/typescript_zh.md

interface Action<T> {
    payload?: T;
    type: string;
}

class EffectModule {
    count = 1;
    message = "hello!";

    delay(input: Promise<number>) {
        return input.then(i => ({
            payload: `hello ${i}!`,
            type: 'delay'
        }));
    }

    setMessage(action: Action<Date>) {
        return {
            payload: action.payload!.getMilliseconds(),
            type: "set-message"
        };
    }
}

答案：

1.首先要將方法給解出來：

type MethodName<T> = {
    [F in keyof T]: T[F] extends Function ? F : never;
}[keyof T];

2.其次將源函數和目標函數做一個對比：

type asyncMethod<T, U> = (input: Promise<T>) => Promise<Action<U>>;
// 轉化為
type asyncMethodConnected<T, U> = (input: T) => Action<U>;

type syncMethod<T, U> = (action: Action<T>) => Action<U>;
// 轉化為
type syncMethodConnected<T, U> = (action: T) => Action<U>;

3.用infer來推導類型，做轉發：

type EffectMethodAssign<T> = T extends asyncMethod<infer U, infer V> ? asyncMethodConnected<U, V> : T extends syncMethod<infer U, infer V> ? syncMethodConnected<U, V> : never;

4.將兩個優化結合：

type Connect = (module: EffectModule) => {
    [F in MethodName<typeof module>]: EffectMethodAssign<typeof module[F]>
};

聯合類型

type UnionToIntersection<U> = 
    (U extends any ? (k: U) => void : never) extends ((k: infer I) => void) ? I : never;

function mixIt<T extends any[]>(...args: T): UnionToIntersection<T[number]>{ 
    let mixin: any =  {};

    args.forEach( obj => {
        for(let key in obj) {
            if( ! mixin.hasOwnProperty(key) ) {
                mixin[key] = obj[key];
            }
        }
    });

    return mixin;
}

class X {x: number = 7;}
class Y {y: string = 'ok';}
class Z {z: boolean = false;}

let x = new X;
let y = new Y;
let z = new Z;

let xy = mixIt(x, y);
let xyz = mixIt(x, y, z);

解構

class Plugin {}
class LandingPlugin extends Plugin {
    a: string;
}
class ShareCore extends Plugin {
    b: string;
}

interface PluginConfig<M> {
    config?: any;
    bindings?: Array<keyof M>; 
};
export type PluginOption<M> = [ConstructorOf<M>, PluginConfig<M>?, any?, boolean?];
function ReinforcePage5<T extends Plugin[]>(c: {
    pluginOptions: [
        ...{[K in keyof T]: PluginOption<T[K]>}
    ]
}): void {};

ReinforcePage5({
    pluginOptions: [
        [LandingPlugin, {
            bindings: ['a']
        }],
        [ShareCore, {
            bindings: ['b']
        }]
    ]
});