算数交换(针对的是Number,或者类型可以转换为数字的变量类型)
function swap(a, b) { a = a + b; b = a - b; a = a - b; }
解构赋值
[a, b] = [b, a];
借用声明第三变量
let x,a = 'a',b = 'b'; x = a a = b b = x