刚刚的pdd笔试的几个题
1、a标签的四个伪类:link,visited,hover,active,并且最好按照上面顺序来写,防止覆盖
2、清除浮动
3、数组展开
const flat = function(arr, depth) {return arr.reduce((res, cur) => {if(depth && cur instanceof Array) {return [...res, ...flat(cur, depth - 1)]} else {return [...res, cur]}}, [])}