TypeScript 函數

TypeScript 函數

函數類型

爲函數定義類型

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

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

使用這種方式，爲函數定義返回的類型

function add(x, y) {
    return x + y;
}
var myAdd = function (x, y) {
    return x + y;
};
//# sourceMappingURL=out.js.map

書寫函數類型

let myAdd: (baseValue: number, increment:number)=>number = 
    function(baseValue: number, increment: number): number {
        return baseValue + increment;
}

書寫函數類型，表明形參爲baseValue和increment兩個都爲number類型，返回的也一樣爲number類型。

推斷類型

// 賦值語句一邊有類型，而另外的一邊沒有類型，此時會自動識別出類型
let myAdd = function(x:number, y:number):number{
    return x + y;
}

let myAdd1:(baseValue: number, increment:number) => number =
function(x,y){
    return x + y;
}

會自動推斷出類型

可選參數 默認參數

不能傳遞null和undefined做爲參數。

// 可選參數 使用？
function buildName(firstName:string, lastName?:string){
    if (lastName)
        return firstName + " " + lastName;
    else
        return firstName;
}

let result1 = buildName("Bob");
let result2 = buildName("bod", "adams");

剩餘參數

function buildName(firstName:string, ...restOfName:string[]){
    return firstName + " " + restOfName.join(" ");    // 進行字符串的拼接
}

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

function buildName(firstName) {
    var restOfName = [];
    for (var _i = 1; _i < arguments.length; _i++) {
        restOfName[_i - 1] = arguments[_i];
    }
    return firstName + " " + restOfName.join(" "); // 進行字符串的拼接
}
var employeeName = buildName("Joseph", "Samuel", "Lucas");
//# sourceMappingURL=out.js.map

this 箭頭函數保存建立時調用的

// 箭頭函數能保存函數建立時的this的值，不是調用值
let deck = {
    suits: ["hearts", "spades", "clubs", "diamonds"],
    cards:Array(52),
    createCardPicker:function(){
        return ()=>{
            let pickedCard = Math.floor(Math.random() * 52);
            let pickedSuit = Math.floor(pickedCard / 13);

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

重載

function pickCard(x):any {
    if (typeof x == "object"){
        let pickedCard = Math.floor(Math.random());
        return pickedCard;
    }
    else if (typeof x == "number"){
        let pickedSuit = Math.floor(x);
        return { x: x };
    }
}

使用if語句便可