假定数组为： [1,3,8,69,'ac','ad']，每隔1s中输出数组中的内容
方法一：es5写法：自执行函数
function count(){
var arr = [1,3,8,69,'ac','ad']
for (var i=0; i<arr.length; i++) {
(function(i){
setTimeout(() => console.log(arr[i]), 1000)
})(i)
}
}
count()方法二：es6块级作用域let
function count(){
var arr = [1,3,8,69,'ac','ad']
for (let i=0; i<arr.length; i++) {
setTimeout(() => console.log(arr[i]), 1000)
}
}
count()
