TypeScript 函数

函数类型

为函数定义类型

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

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

使用这种方式，为函数定义返回的类型

function add(x, y) {
    return x + y;
}
var myAdd = function (x, y) {
    return x + y;
};
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书写函数类型

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

书写函数类型，代表形参为baseValue和increment两个都为number类型，返回的也同样为number类型。

推断类型

// 赋值语句一边有类型，而另外的一边没有类型，此时会自动识别出类型
let myAdd = function(x:number, y:number):number{
    return x + y;
}

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

会自动推断出类型

可选参数 默认参数

不能传递null和undefined作为参数。

// 可选参数 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");

剩余参数

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

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(" "); // 进行字符串的拼接
}
var employeeName = buildName("Joseph", "Samuel", "Lucas");
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this 箭头函数保存创建时调用的

// 箭头函数能保存函数创建时的this的值，不是调用值
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 };
        }
    }
}

重载

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语句即可

TypeScript 函数

原文：https://www.cnblogs.com/melovemingming/p/9880423.html