ES6新特性_函数参数的默认值

ES6_形参初始值，具有默认值的参数一般位置要靠后(潜规则)

// c 默认值
function add(a,b,c=3){
    return a + b + c;
}
console.log(add(1,2)); // 6

ES6_与解构赋值结合

// 一般写法
function connect(options){
    let host = options.host;
    let username = options.username;
    let password = options.password;
    let port = options.port;
    console.log(host,username, password, port);
}

// 调用
connect({host:'localhost', username:"root", password:"123456", port: "3306"});
// localhost root 123456 3306

ES6里的写法

// host 设置了默认值
function connect({host='127.0.0.1', username, password, port}){
    console.log(host,username, password, port);
}

// 传了host
connect({host:'localhost', username:"root", password:"123456", port: "3306"});
// localhost root 123456 3306

// 未传host
connect({username:"root", password:"123456", port: "3306"});
// 127.0.0.1 root 123456 3306