函数

/** 为函数定义类型 */

// 为函数的参数指定类型，为函数的返回值指定类型
function add(x: number, y: number): number {
    return x + y;
}

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

// 完整的函数
let myAdd2: (x: number, y: number) => number = function (x: number, y: number): number{ return x + y }

let myadd3: (x: number, y: number) => number = function (x: number, y: number) { return x + y }

let myadd4: (b: number, y: number) => number = function (x: number, y: number) { return x + y; }

let myadd5: (x:number, y: number) => number=function(x,y){return x+y}

// 可选参数和默认参数：ts里传入一个函数的参数个数必须与函数期望的参数个数一致

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

let result = buildName("jsck", "bruce")
let result1 = buildName("jsck")
console.log(result1)

// 可选参数必须放在后面
function buildName2(firstName: string, lastName?: string) {
    return firstName + " " + lastName
}

let result2 = buildName2("jsck", "bruce")
let result3 = buildName2("jsck")
console.log(result2)
console.log(result3)

// 默认参数，当用户没有传值或者传递的值是undefined的时候生效
function buildName3(firstName: string, lastName="smith") {
    return firstName + " " + lastName
}

let result4= buildName3("bob", undefined)

// 剩余参数
function buildName4(firstName: string, ...restOfName: string[]) {
    return firstName + ',' + restOfName.join(",")
}

let employeeName = buildName4("xiaoju", "weimeng", "ruixin", "tengying")

console.log(employeeName)