functions.md

functions

Named function (명명)

// Named function
function add(x, y) {
    return x + y;
}

Anonymous function (익명)

// Anonymous function
let myAdd = function(x, y) { return x+y; };

Typing the function

function add(x: number, y: number): number {
    return x + y;
}

let myAdd = function(x: number, y: number): number { return x+y; };

매개 변수와 반환 유형 사이에 굵은 화살표 ( => )를 사용하여 반환 유형을 명확하게합니다. 앞에서 언급했듯이 이것은 함수 유형에서 필수적인 부분이므로 함수가 값을 반환하지 않으면 void 를 사용합니다.

Optional and Default parameters

function buildName(firstName: string, lastName: string) {
    return firstName + " " + lastName;
}

let result1 = buildName("Bob");                  // error, too few parameters
let result2 = buildName("Bob", "Adams", "Sr.");  // error, too many parameters
let result3 = buildName("Bob", "Adams");         // ah, just right

function buildName(firstName: string, lastName?: string) {
    if (lastName)
        return firstName + " " + lastName;
    else
        return firstName;
}

let result1 = buildName("Bob");                  // works correctly now
let result2 = buildName("Bob", "Adams", "Sr.");  // error, too many parameters
let result3 = buildName("Bob", "Adams");         // ah, just right

function buildName(firstName: string, lastName = "Smith") {
    return firstName + " " + lastName;
}

let result1 = buildName("Bob");                  // works correctly now, returns "Bob Smith"
let result2 = buildName("Bob", undefined);       // still works, also returns "Bob Smith"
let result3 = buildName("Bob", "Adams", "Sr.");  // error, too many parameters
let result4 = buildName("Bob", "Adams");         // ah, just right

Rest Parameters

function buildName(firstName: string, ...restOfName: string[]) {
    return firstName + " " + restOfName.join(" ");
}

let employeeName = buildName("Joseph", "Samuel", "Lucas", "MacKinzie");

function buildName(firstName: string, ...restOfName: string[]) {
    return firstName + " " + restOfName.join(" ");
}

let buildNameFun: (fname: string, ...rest: string[]) => string = buildName;

this

let deck = {
    suits: ["hearts", "spades", "clubs", "diamonds"],
    cards: Array(52),
    createCardPicker: function() {
        return function() {
            let pickedCard = Math.floor(Math.random() * 52);
            let pickedSuit = Math.floor(pickedCard / 13);

            return {suit: this.suits[pickedSuit], card: pickedCard % 13};
        }
    }
}

let cardPicker = deck.createCardPicker();
let pickedCard = cardPicker();

alert("card: " + pickedCard.card + " of " + pickedCard.suit);

createCardPicker에 의해 생성 된 함수에서 사용되는 this가 deck 객체 대신 window로 설정되기 때문에 위 code는 동작하지 않습니다.

let deck = {
    suits: ["hearts", "spades", "clubs", "diamonds"],
    cards: Array(52),
    createCardPicker: function() {
        // NOTE: the line below is now an arrow function, allowing us to capture 'this' right here
        return () => {
            let pickedCard = Math.floor(Math.random() * 52);
            let pickedSuit = Math.floor(pickedCard / 13);

            return {suit: this.suits[pickedSuit], card: pickedCard % 13};
        }
    }
}

let cardPicker = deck.createCardPicker();
let pickedCard = cardPicker();

alert("card: " + pickedCard.card + " of " + pickedCard.suit);

화살표 함수는 호출 된 곳이 아닌 함수가 생성 된 곳을 캡처합니다.