ES6 从入门到精通 # 04：函数之默认值、剩余参数

// es5 写法
function add(a, b) {
  a = a || 666;
  b = b || 777;
  return a + b;
}
console.log(add());
function add2(a, b = 666) {
  return a + b;
}
console.log(add2(2));

function getVal(val) {
  return val + 1;
}
function add3(a, b = getVal(6)) {
  return a + b;
}
console.log(add3(3));

// es5
function getBlogInfo(obj) {
  let result = Object.create(null);
  for(let i = 1; i < arguments.length; i++) {
    result[arguments[i]] = obj[arguments[i]];
  }
  return result;
}
let blog = {
  name: "凯小默的博客",
  author: "kaimo",
  year: "2017"
}
let blogData = getBlogInfo(blog, "name", "author", "year");
console.log(blogData);

// es6
function getBlogInfo(obj, ...keys) {
  console.log(keys);
  let result = Object.create(null);
  for(let i = 0; i < keys.length; i++) {
    result[keys[i]] = obj[keys[i]];
  }
  return result;
}
let blog = {
  name: "凯小默的博客",
  author: "kaimo",
  year: "2017"
}
let blogData = getBlogInfo(blog, "name", "author", "year");
console.log(blogData);

function checkArgs(...args) {
  console.log(args); // 真实数组
  console.log(arguments); // 伪数组
}
checkArgs("name", "author", "year");