参考网址：https://www.tslang.cn/docs/handbook/functions.html 可选参数和默认参数

    • 源码
    • Functions.ts ``` //可选参数 // function buildName(firstName:string,lastName:string) { // return firstName + “ “ + lastName; // } // let result1 = buildName(‘xiaochuan’,’xiaoming’);//‘xiaochuan xiaoming’ // let result2 = buildName(‘xiaochuan’);//这里在编译时直接就报错了 Functions.ts(5,15): error TS2554: Expected 2 arguments, but got 1. // let result3 = buildName(‘xiaochuan’,’xiaoming’,’xiaohong’);//这里在编译时直接就报错了 Functions.ts(6,15): error TS2554: Expected 2 arguments, but got 3.

    //上面的话传递参数的数量就必须得是 两个

    //下面是不确定几个参数时的写法 //在参数名称的后面加一个 ? 号 使这个参数变为可选项 // function buildName(firstName:string,lastName?:string) { // //在这里做判断返回想应的返回值 // if(lastName){ // return firstName + “ “ + lastName; // }else{ // return firstName; // } // } // let result1 = buildName(‘xiaochuan’,’xiaoming’);//‘xiaochuan xiaoming’ // let result2 = buildName(‘xiaochuan’);//这里编译时就直接通过了 // let result3 = buildName(‘xiaochuan’,’xiaoming’,’xiaohong’);//三个参数还是同样的报错，因为超出了参数的定义数量

    //默认参数 function buildName(firstName:string,lastName=”xiaochuan”){ return firstName + “ “ + lastName; } let result1 = buildName(‘xiaochuan’);//编译通过 返回 ‘xiaochuan xiaochuan’ let result2 = buildName(‘xiaochuan’,’xiaoming’);//编译通过 返回 ‘xiaochuan xiaoming’ // let result3 = buildName(‘xiaochuan’,’xiaoming’,’xiaohong’);//编译失败 Functions.ts(33,15): error TS2554: Expected 1-2 arguments, but got 3. document.getElementById(‘pid’).innerHTML = result1 + “
    “ + result2;

    2. - index.html

    <!DOCTYPE html>

    ```

    • 效果图

    1514821767(1).jpg