타입스크립트 핸드북 9장 - (고급 타입) 교차 타입, 유니언 타입

class Sprite {
	name = "";
	x = 0;
	y = 0;
	
	constructor(name: string) {
		this.name = name;
	}

	getName(): string {
		return this.name;
	}
}

// To get started, we need a type which we'll use to extend
// other classes from. The main responsibility is to declare
// that the type being passed in is a class.

type Constructor = new (...args: any[]) => {};

// This mixin adds a scale property, with getters and setters
// for changing it with an encapsulated private property:

function Scale<TBase extends Constructor>(Base: TBase) {

	return class Scaling extends Base {
		// Mixins may not declare private/protected properties
		// however, you can use ES2020 private fields
		_scale = 1;
		
		setScale(scale: number) {
			this._scale = scale;
		}

		get scale(): number {
			return this._scale;
		}
	};
}

// Compose a new class from the Sprite class,
// with the Mixin Scale applier:

const EightBitSprite = Scale(Sprite);
const flappySprite = new EightBitSprite("Bird");
flappySprite.setScale(0.8);
console.log(flappySprite.scale);  // 0.8
console.log(flappySprite.getName()); // "Bird"

function extend<First, Second>(first: First, second: Second): First & Second {
    const result: Partial<First & Second> = {};
    for (const prop in first) {
        if (first.hasOwnProperty(prop)) {
            (result as First)[prop] = first[prop];
        }
    }
    for (const prop in second) {
        if (second.hasOwnProperty(prop)) {
            (result as Second)[prop] = second[prop];
        }
    }
    return result as First & Second;
}

class Person {
    constructor(public name: string) { }
}

interface Loggable {
    log(name: string): void;
}

class ConsoleLogger implements Loggable {
    log(name) {
        console.log(`Hello, I'm ${name}.`);
    }
}

const jim = extend(new Person('Jim'), ConsoleLogger.prototype);
jim.log(jim.name);

function padLeft(value: string, padding: any) {
    if (typeof padding === "number") {
        return Array(padding + 1).join(" ") + value;
    }
    if (typeof padding === "string") {
        return padding + value;
    }
    throw new Error(`Expected string or number, got '${padding}'.`);
}

padLeft("Hello world", 4); // "    Hello world"를 반환합니다.