箭头表达式

let sum = (num1, num2) => num1 + num2;

let sum1 = (num1, num2) => {
    //多行必须花括号包裹
    let num3 = num1 + num2;
    return num3;
 }
let demo = () => { }

let demo1 = arr1 => {
    //一个参数 
    console.log(arr1)
}

let demo2 = [1, 2, 3, 4, 5, 6];
console.log(demo2.filter(value=>value%2==0))

function demo3(name) { 
    this.name = name;
    setInterval(function () {
        console.log('---'+this.name);
     },1000);
}
let demo_4 = new demo3('zhangsan');

function demo4(namea) { 
    this.namea = namea;
    setInterval(() => {
        console.log(this.namea)
    },1000)
}
let demo5 = new demo4('lishi');