SOURCE

console 命令行工具 X clear

                    
>
console
var btn=document.getElementById('btn')
var btn1=document.getElementById('reset')
var tx=document.getElementsByTagName('span')
var content=document.getElementById('content')
var arr=[];
var n=0;


//btn.disabled=true
btn.onclick=function(){7
    var x=Math.floor(Math.random()*(49-1+1)+1)
    x=PrefixZero(x,2);
   
        content.innerHTML+='<span>'+x+'</span>'
    n++;
    if(n==7){
        this.disabled=true;
        tx[n-1].className='active'
    }
    console.log(tx.length)
}

btn1.onclick=function(){
    content.innerHTML="";
    btn.disabled=false;
    n=0;
}


function PrefixZero(num, n) {
    return (Array(n).join(0) + num).slice(-n);
}






<input id="btn" type="button" value="开始" />
<input id="reset" type="button" value="重置" />
<input id="third" type="button" value="三" />
</br> </br> </br>
<div id="content">

</div>



span{
    width:30px;
    height:30px;
    line-height:30px;
    display:block;
    background:skyblue;
    text-align: center;
    margin:10px;
    border-radius: 50%;
    float:left;
    
}


.active{
    background:red;
}