函数扩展

/*
1. 形参的默认值
2. 可变参数
3. 箭头函数
 */

    //1. 形参的默认值
    function Point(x = 1,y = 2) {
        this.x = x;
        this.y = y;
    }

    var p = new Point(3, 4);
    console.log(p);
    p = new Point();
    console.log(p);

    //2. 可变参数
    function add(... values) {
        let sum = 0;
        for(value of values) {
            sum += value;
        }
        return sum;
    }
    console.log(add(2, 5, 4));

    //3. 箭头函数
        //使用'箭头'(=>)定义函数
    var fun = function (v) {
        return v+3;
    }
    var fun2 = v => v+3;


    console.log(fun2(3));

    var fun3 = (num1, num2) => num1+num2;//=>后面为返回值
    console.log(fun3(3, 5));

    [1, 3, 5forEach].(function (element) {
       console.log(element*element);
    });

    [1, 3, 5].forEach(element => console.log(element*element));