ES6 一些特性

# 解構

const nums = [1,2,3];
const first = nums[0];
const second = nums[1];

可以改用

const [first, second] = nums;

# 要只取第二個

const [, second] = nums;

# 預設值
# 原本 fourth 應該是 undefined, 但透過後面的 assign 給定預設值
const [, second, third, fourth = 0] = nums;

# 值交換

let a = 1;
let b = 2;
[a, b] = [b, a];

# 剩餘部分

const nums = [1,2,3,4];
const [first, ...other] = nums;

# nums => [2,3,4]


# 物件解構
const points = {x:1,y:2};
# x = 1
const {x} = points;

# rename x to px (只限定物件, 不可以用在Array)
const {x:px} = points;

Expression 表達式
Statement 陳述式

Expression => 可以用 ()包起來的
Statement => 無法用()包起來的
ex:
if (1>2)

表達式

1+2;
const a;
a+2;

字串模板

字串模板內可以放入表達式

function greet(name, days) {
  console.log(`Hello, ${name}! It has been ${days * 24} hours not seen you!`);
}

# or

function greet(name, days) {
  console.log(`Hello, ${name}! ${(days < 7) ? '' : 'Long time no see'}`);
}

字串模板也支援多行字串

const str = `
123456
12345
1234567
`;

arrow function 內的 this 會等同於外部的this

const a = () => {
  // 此處的this等同於外面 console.log(this)的this
  const aa = () => {
    // 此處的this也等同於外面 console.log(this)的this
  }
}
console.log(this)