ES6新特性--允许给函数参数赋初始值

1. 函数形参赋初始值

// 1. 形参赋初始值
function increment(m, n, p = 0) {
  return m + n + p
}
// let result = increment(1, 3, 4)
let result = increment(1, 3)
console.log(result)

2. 与解构赋值相结合

// 2. 与结构赋值相结合
function connect ({ host = '127.0.0.1', username, password, port }) {
  console.log(host)
  console.log(username)
  console.log(password)
  console.log(port)
}
// 调用connect 传入一个对象
connect ({
  host: 'localhost',
  username: 'root',
  password: 'root',
  port: 3306
})