JavaScript实现不重复随机抽号功能详解

<body>
  <input type="text" id="txt" placeholder="请在里面输入号码最大值！">
  <input type="button" id="btn" value="抽号">
  <div>
   <span>结果：</span>
   <span id="result"></span>
  </div>
  <div>
   <span>已抽取：</span>
   <span id="exist"></span>
  </div>
  <script type="text/javascript">
   var oBtn = document.getElementById("btn");
   var oTxt = document.getElementById("txt");
   var oRes = document.getElementById("result");
   var oExi = document.getElementById("exist");
   var arr = []; //存放座号 
   oBtn.onclick = function() {
    getSeat(oTxt.value);
   }
   function getSeat(maxnum) {
    for(var i = 0; i < maxnum; i++){
     var num = Math.floor(Math.random() * maxnum) + 1;
     var j;
     for(j = 0; j < arr.length; j++) {
      if(num == arr[j])
       break;
     }
     if(j == arr.length) {
      arr.push(num);
      oRes.innerHTML = num;
      oExi.innerHTML = arr;
      return;
     }
    }
   }
  </script>
 </body>