获取元素和循环

  window.onload = function(){
      var lis = docment.getElementsByTagName("li");
      lis[0].style.backgroundColor = "gold";
      lis[1].style.backgroundColor = "gold";
}

document.getElementsByTagName(); 标签获取元素

循环

for循环

window.onload = function(){
    var olist = document.getElementById("list01");
    var ali = olist.getElementsByTagName("li");
    for(var i = 0; i <8; i++){
          if (i%2 == 0){
              all[i].style.backgroundColor = "gold";
    }
  }
  i++;
}

while循环

var i = 0;
while (i< ali.length){
        if(i%2 == 0){
              ali[i].style.backgroundColor = "gold";
    }
  i++;
};

do while循环

var i = 0;
      do{
          if (i %2==0){
                ali[i].style.backgroundColor = "gold";
  }
  i++;
  }while (i < ali.length);
}

while和do while 的区别:

do while 是大括号里无论如何都先执行一次,执行完再判断是否成立
while是先判断是否成立,然后在执行大括号的内容