小编Ah *_*uan的帖子

我想在单击时将心形变为黑色，但更改 .heart 的颜色不会影响它的 :before :after 选择器。有什么办法吗？

.heart {
  background-color: red;
  height: 60px; /*dimension of the square*/
  position: relative;
  top: 40px; /*position from top*/
  transform: rotate(-45deg); /*negative = counter clockwise, put 0 to try*/
  width: 60px; /*dimension of the square*/
  transition: all 1s ease; /*length of animation*/
}

.heart:before,
.heart:after {
  content:""; /*kosong, for it to exist*/
  background-color: red;
  border-radius: 50%; /*perfect round curve*/
  height: 60px; /*dimension of the shape*/
  position: absolute;
  width: 60px; /*dimension of the shape*/
}

.heart:before { …

我正在尝试了解此代码段如何使多级/嵌套数组扁平化

有人可以帮忙详细说明吗？谢谢

var flatten = function(a, shallow,r){
  if(!r){ r = []}     //what does the exclamation mark mean here?...

if (shallow) {
  return r.concat.apply(r,a);  //I can't find what's .apply for concat method
  }

   for(var i=0; i<a.length; i++){
        if(a[i].constructor == Array){
            flatten(a[i],shallow,r);
        }else{
            r.push(a[i]);
        }
    }
    return r;
}

alert(flatten([1, [2], [3, [[4]]],[5,6]]));