TypeScript函数

TypeScript 函数-可选和默认参数

//可选参数
function vvvv(first: string, second: string) {
    return (first + ":" + second);
}
let res1 = vvvv("aaa", "aaa");//right
//参数个数问题
// let res2 = vvv("aa");//error
// let res3 = vvv("aa","bbb","sss");//error
//当前不确定传的参数是一个还是两个(不可超过参数总个数)
function vvvvx(first: string, second?: string) {
    // return (first + ":" + second);
    if (second == null) {
        return first;
    } else {
        return (first + ":" + second);
    }
}
let res4 = vvvvx("aaa");
let res5 = vvvvx("aaa", "sss");
alert(res4 + ":::::::::::" + res5);
//默认参数 给参数直接设置一个默认值
//
function vvvvvx(first: string, second = "aaa") {
    return (first + ":" + second);
}
let res10 = vvvvvx("bbb");//默认第二个参数为aaa
let res11 = vvvvvx("bbb","cc");//默认第二个参数为cc
//let res12 = vvvvvx("bbb","aaa","ccc");//error
// document.getElementById("pid").innerHTML = res10+":"+res11;
alert(res10 + ":::::::::::" + res11);

　　TypeScript 函数-可变参数

//可选参数或者既定参数，个数都是一定的，在可变参数的rest parameter 可以不受参数个数的限制
类型受限
//...second: string[] 可变参数
function vvvv(first: string, ...second: string[]) {
    return (first + ":" + second.join("_"));
}