function $(className) {
  var newClassName = className.split(" ");
  if (newClassName.length > 1) {
    var father = newClassName[newClassName.length - 2];
    var childrenList = document.querySelector(father).children;

    var arr = Array.from(childrenList).filter(function (el){
      if (
        el.className.indexOf( (newClassName[newClassName.length-1]).replace(".", "") ) > -1
        ||
        el.tagName.toLowerCase() == newClassName[newClassName.length-1]
      ) {
        return el;
      }
    });

    if (arr.length > 1) {
      return document.querySelectorAll(className)
    } else if (arr.length == 1){
      return document.querySelector(className)
    } else {
      throw new Error(`${className} 不存在，请检查`)
    }

  } else {
    return document.querySelector(newClassName);

  }
}

function scroll(callback) {
  $("body").onscroll = () => {
    let scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
    let clientHeight = document.documentElement.clientHeight || document.body.clientHeight;
    let scrollHeight = document.documentElement.scrollHeight || document.body.scrollHeight;

    if(scrollHeight > clientHeight && scrollTop + clientHeight === scrollHeight) {
      callback()
    }
  }
}


function query(name) {
  var reg = new RegExp("(^|&)"+ name +"=([^&]*)(&|$)");
  var r = window.location.search.substr(1).match(reg);
  if(r!=null)return  unescape(r[2]); return null;
}