不使用第三个变量交换两个数的值

第一种

        var a = 1,
            b = 2;
        a = a + b; // a = 3, b = 2
        b = a - b; // a = 3, b = 1
        a = a - b; // a = 2, b = 1
        console.log(a,b);

第二种

//ES6解构赋值

        let a = 1,
            b = 2;
        [a, b] = [b, a];
        console.log(a, b);