window.onload=function(){
            var lis = document.getElementByTagName('li');
            lis[0].style.backgroundColor = 'gold';
            lis[1].style.backgroundColor = 'gold';
    }

• document.getElementsByTagName(),标签获取元素

循环

1.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){
                                  ali[i].style.backgroundColor = 'gold';  
                      }            
            }
            i++;
    }

2.while循环

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

3.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，才执行判断是否成立
• while是先判断是否成立，然后在执行大括号里的内容