8.ES6 函数参数默认值

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ES6 函数参数默认值

ES6 允许给函数参数赋值初始值

1.形参初始值, 具有默认值的参数, 一般位置要靠后

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let add = (a, b, c=6) => a + b + c;
let result1 = add(1, 2, 5);
console.log(result1);
// 8

let result2 = add(1, 2);
console.log(result2);
// 9

let result3 = add(1);
console.log(result3);
// NaN

2.可以与解构赋值结合

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function connect({host, port="3306", username, password}) {
    console.log(host);
    console.log(port);
    console.log(username);
    console.log(password);
    /**
     * 127.0.0.1
     * 3306
     * root
     * 123456
     */
}
connect({
    host: "127.0.0.1",
    // port: "1521",
    username: "root",
    password: "123456"
});